Supercritical Carbon Dioxide Medium Research Articles

Raziskave o trajnostni proizvodnji tekstila: brezvodno barvanje poliestrskih in recikliranih poliestrskih tkanin

Due to water limitations and the growing global demand for raw materials, manufacturers and consumers are seeking more environmentally friendly alternatives. Polyester, a non-biodegradable fibre derived from petroleum, can be replaced with recycled polyester (r-PET), a sustainable alternative that reduces environmental impacts through the reuse of materials. The textile finishing industry, known for its high water and energy consumption, is calling for the development of low-water-consumption technologies. One innovative approach involves waterless dyeing procedures using a supercritical carbon dioxide (scCO2) medium that is particularly suitable for dyeing synthetic fibres. To assess its effectiveness, a study compared traditional water dyeing with scCO2 medium dyeing on woven fabrics made from both polyester (PET) and recycled polyester (r-PET) fibres with varying weights. After conducting tests on the dyed fabrics, the data revealed that r-PET fabrics dyed using a supercritical carbon dioxide (scCO2) medium appeared darker than fabrics dyed using traditional water dyeing techniques. Moreover, r-PET fabrics demonstrated better colour fastness. Notably, the K/Ssum values (measurement of colour intensity) of r-PET fabrics were at least as good as those of PET-based fabrics in all cases of dyeing, while the fastness values were similar for both PET and r-PET fabrics.

Improved biocatalytic activity of steapsin lipase in supercritical carbon dioxide medium for the synthesis of benzyl butyrate: A commercially important flavour compound

Enzymatic synthesis of flavours, fragrances and food additives compounds have great demand and market value. Benzyl butyrate is commercially important flavour and food additive compound having global use around 100 metric tons/year and widely used in various industrial sectors. However, industrial synthesis of food additive benzyl butyrate is carried out by conventional chemical process which demands for the green biobased sustainable synthetic process. The present work reports steapsin catalyzed synthesis of benzyl butyrate for the first time in supercritical carbon dioxide (Sc-CO2) reaction medium. All reaction variables are optimized in details to obtain competent conversion of 99% in Sc-CO2 reaction medium. The developed steapsin catalyzed synthesis in Sc-CO2 medium offered almost four-fold higher conversion to benzyl butyrate than organic (conventional) solvent. The steapsin biocatalyst was effectually recycled up to five reaction cycles in Sc-CO2 medium. Moreover, the developed steapsin catalyzed protocol in Sc-CO2 medium was extended to synthesize different TEN industrially significant flavour fragrance compounds that offers 99% conversion and three to five-folds higher conversion than organic (conventional) medium. Thus, the present steapsin catalyzed protocol offered improved synthesis of various commercially significant flavour compounds in Sc-CO2. medium.

The effect of surface modification with ozone in waterless (ScCO2) dyeing o polyester

In this study, ozonation was carried out prior to dyeing 100% polyester fabrics through spray application (without the use of water) at various durations and with different gas flow rates. The ozonated fabrics were dyed with Dianix Dry XF2 Rubine (disperse dye) in conventional and supercritical carbon dioxide (scCO2) medium. The main objective of the study is to investigate the colour efficiency of the ozone modified polyester fabric in waterless dyeing. Hydrophilicity, colour measurement, tensile strength, fastness tests, SEM analyses were performed on the samples. The results of dyeing the samples in a waterless medium after ozonation revealed higher colour strength (K/S) and better fastness test results with breaking strength values than conventionally dyed fabrics.

Phase equilibria of binary and ternary mixtures with poly(styrene-co-hexafluorobutyl methacrylate) and solvents at high pressure and temperature

This paper presents the synthesis of the fluoric copolymer poly(styrene-co-2,2,3,4,4,4-hexafluorobutyl methacrylate) [P(styrene-co-HFBMA)] through dispersed phase polymerization in a supercritical carbon dioxide (sc-CO2) medium. The physiochemical characteristics of P(styrene-co-HFBMA) were extensively studied by varying the styrene to HFBMA mole ratios (40:1, 25:1, and 20:1) and 2,2'-Azobisisobutyronitrile (AIBN) initiator at different mass percentages (mass%) from 1 to 4, along with the mean molecular mass (Mm). Phase transition data were reported for two-component and three-component P(styrene-co-HFBMA) in sc-C3H8, C3H6, C4H10, and C4H8, encompassing temperature “T” and pressure “P” limits (∼341 to ∼459) K, and (∼21 to ∼185) MPa, respectively. The phase behavior of the P(styrene-co-HFBMA) + solvent mixtures displayed an upper critical solution temperature (UCST) type behavior with a declining gradient. Equilibria curves were measured for the P(styrene-co-HFBMA) + (C3H10/C3H6) + CH3OCH3(i.e., DME) (25:1, AIBN mass%: 2.0) system in “P-T” phase diagram, spanning from the UCST region to LCST region at DME mass% ranging from 0.0 to 68.5. Additionally, solubility curves at “P”: up to ∼148 MPa and “T”: from ∼450 K to ∼350 K showed a shift from a declining slope to an inclined slope within the 0.0 to 60.3 mass% range for the P(styrene-co-HFBMA) (mole ratio:25:1; AIBN mass%: 2.0) + (C4H10/C4H8) + DME system. These findings provide valuable insights into the phase behavior and solubility characteristics of the P(styrene-co-HFBMA) copolymer in different sc-solvent mixtures.

Solubility of di-cyclohexylhydrogen phosphonate in supercritical carbon dioxide medium: Application towards the recovery of uranium from aqueous solution

Hydrogen phosphonates are di-esters of phosphonic acids and are widely employed as ligands for recovery of actinide species from different matrices. An alicyclic hydrogen phosphonate, namely, di-cyclohexylhydrogen phosphonate (DCyHeHP) is synthesized; its solubility in supercritical carbon dioxide medium is evaluated towards development of a supercritical fluid extraction (SFE) method for recovery of actinide species. The solubility experiments were carried out at three isotherms (313 K, 323 K, and 333 K) with pressure varying from 10 MPa − 20 MPa, using a dynamic flow method. The mole fraction solubility ranges from 0.2 × 10-3 to 102 × 10-3 in the investigated region. The experimental solubility data was modelled using five semi-empirical equations; Mendez-Santiago, Chrastil, del Valle, Adachi Lu and Sparks equations. The experimental data was found to be self-consistence based on Mendez-Santiago equation. The prediction ability of these models was compared using absolute average relative deviation (AARD) and corrected Akaike Information Criterion (AICc). Among the models employed in the present study, Adachi Lu equation found to better with an AARD and AICc value of 4.2% and 87.2 respectively. Based on the solubility data, SFE method was developed for the selective recovery of uranium from representative fission product elements from an aqueous solution using SCCO2 containing DCyHeHP.

A MATHEMATICAL STUDY ON THE EFFECT OF MOLAR RATIOS OF THE REACTANTS FOR BIODIESEL PRODUCTION IN SC-CO2 MEDIUM

The present global situation is so alarming that the conventional energy resources are decaying day by day. This adverse situation encourages us to introduce unconventional and sustainable energy resources like biodiesel. The main source of biodiesel is the non-edible vegetable oil (Jatropha curcas oil) and it is produced by chemical catalytic method. But recently supercritical method has also been proposed as an alternative cost-effective method for its production. A good quality of biodiesel can be produced in a Supercritical-Carbon dioxide medium. The productivity of biodiesel preparation through supercritical method depends on molar ratio of the reactants (water and methanol). In this research article, a set of nonlinear differential equations has been formulated based on concentrations of Triglyceride, Diglyceride, Monoglyceride, Methanol, Free fatty acid, Water, Glycerol and Biodiesel. Our study is based on the effect of the molar ratios of the reactants and how we can get a cost-effective production of biodiesel. The validity of our model is attained by experimental results. The analytical results are also verified by our numerical findings

Grafting of Organophosphonic Acid Monolayers on Hydrogen-Terminated Silicon Surface and Secondary Functionalization in Supercritical Carbon Dioxide Media.

The monolayer grafting on the oxide-free Si surface is challenging due to vulnerability of the surface against oxide formation in an ambient atmosphere. Most of the conventional studies focused on organic solvent-based chemistry and solvent and substrate interfaces, and residual solvents after the monolayer grafting play a key role in producing the highly stable monolayers. CO2 in its supercritical state (SCCO2) provides an elegant engineering solution for the problem faced as it can be used as inert processing environment and as carrier fluid for monolayer grafting taking up the role of organic solvents. In this work, monolayers of alkyl organophosphonic acids (OPAs) and functional OPAs were grafted on hydrogen-terminated oxide-free Si surfaces using the SCCO2 process. Grafted monolayers were physically and chemically characterized to verify the successful monolayer formation and determine the nature of the covalent binding configuration on the surface. To broaden the prospects of practical utility of the process and the OPA monolayer, the (3-bromopropyl)phosphonic acid (BPPA) monolayer was demonstrated to undergo secondary functionalization by terminal group substitution to convert the Br terminal group to the OH terminal group and secondary monolayer grafting to assemble 4-fluorothiophenol on top of the BPPA monolayer. The ability of monolayers to sustain secondary functionalization processing qualitatively hints toward ordered and stable monolayers of OPAs. The developed SCCO2 process in this work presents a single-step, green, and scalable method to graft the OPA monolayer on oxide-free Si which can employed in the future for monolayer doping, highly selective biochemical sensors, and targeted biological interactions.

Waterless dyeing of polytrimethylene terephthalate and polybutylene terephthalate fabrics via supercritical carbon dioxide

In this study, polytrimethylene terephthalate (PTT) and polybutylene terephthalate (PBT) samples were dyed n supercritical carbon dioxide (scCO2) medium. Dianix Dry Blue XF2 and CI Disperse Blue 79 were used for dyeing. Pressure and time optimisation trials were conducted, maintaining the temperature constant based on the optimal results obtained from these trials. The color, fastness, and tensile strength values were assessed. For both PTT and PBT fabrics, the closest color values to conventional dyeing were achieved when dyed with CI Disperse Blue 79 at 85 °C and 25 MPa, and with Dianix Dry Blue XF2 at 70 °C and 25 MPa. Notably, when compared to conventionally dyes samples, darker colors were obtained in scCO2 medium after 70 °C when dyeing with Dianix Dry Blue XF2 and after 85 °C when dyeing with CI Disperse Blue 79 compared to conventionally dyed samples.

Sound Insertion Loss Performance of Baffles with Devulcanized Waste Rubber

In this study, the insertion loss of devulcanized waste rubber baffles was evaluated. Acoustic baffles are suitable for reducing noise from the devices or machines by interfering with their emitting sound waves. Knowledge of the acoustic properties of the material used is of significant importance in ensuring the effectiveness of the acoustic properties of the baffle. Basic properties include airborne sound insulation, which is usually determined during laboratory testing. Baffle consists of sound absorbing and sound insulating materials. In this study, plasterboards were used as sound insulating material and devulcanized waste rubber as sound absorbing material. Devulcanization targets mostly the scission of sulphur crosslinks. Devulcanization techniques that have been explored in rubber recycling include thermos-chemical, microbiological, ultrasonic microwave thermos-chemical devulcanization in a supercritical carbon dioxide medium (scCO2). In this study, two types of rubber granules were devulcanized by grinding method and one other type was chemically devulcanized. Three types of rubber granules were mixed together in increasing 25 % proportion steps and glued with patented polyurethane glue. Total of 15 different composition devulcanized waste rubber granule boards were made. Rubber boards were attached together with the plasterboards. Insertion loss of the different composite baffles was measured in semi-anechoic chamber in a purposefully designed stand in 1/3rd-octave bands. The results showed that the insertion loss of the baffles depends mostly on the rubber granule board density. Increasing the density of the rubber board, insertion loss also increased. 5–6 dB insertion loss difference was measured between the most and the least dense rubber granule board baffles.

FLIM imaging revealed spontaneous osteogenic differentiation of stem cells on gradient pore size tissue-engineered constructs

BackgroundThere is an urgent clinical need for targeted strategies aimed at the treatment of bone defects resulting from fractures, infections or tumors. 3D scaffolds represent an alternative to allogeneic MSC transplantation, due to their mimicry of the cell niche and the preservation of tissue structure. The actual structure of the scaffold itself can affect both effective cell adhesion and its osteoinductive properties. Currently, the effects of the structural heterogeneity of scaffolds on the behavior of cells and tissues at the site of damage have not been extensively studied.MethodsBoth homogeneous and heterogeneous scaffolds were generated from poly(L-lactic acid) methacrylated in supercritical carbon dioxide medium and were fabricated by two-photon polymerization. The homogeneous scaffolds consist of three layers of cylinders of the same diameter, whereas the heterogeneous (gradient pore sizes) scaffolds contain the middle layer of cylinders of increased diameter, imitating the native structure of spongy bone. To evaluate the osteoinductive properties of both types of scaffold, we performed in vitro and in vivo experiments. Multiphoton microscopy with fluorescence lifetime imaging microscopy was used for determining the metabolic states of MSCs, as a sensitive marker of cell differentiation. The results obtained from this approach were verified using standard markers of osteogenic differentiation and based on data from morphological analysis.ResultsThe heterogeneous scaffolds showed improved osteoinductive properties, accelerated the metabolic rearrangements associated with osteogenic differentiation, and enhanced the efficiency of bone tissue recovery, thereby providing for both the development of appropriate morphology and mineralization.ConclusionsThe authors suggest that the heterogeneous tissue constructs are a promising tool for the restoration of bone defects. And, furthermore, that our results demonstrate that the use of label-free bioimaging methods can be considered as an effective approach for intravital assessment of the efficiency of differentiation of MSCs on scaffolds.

Investigation of the Spatial Structure of Flufenamic Acid in Supercritical Carbon Dioxide Media via 2D NOESY

The search for new forms of already known drug compounds is an urgent problem of high relevance as more potent drugs with fewer side effects are needed. The trifluoromethyl group in flufenamic acid renders its chemical structure differently from other fenamates. This modification is responsible for a large number of conformational polymorphs. Therefore, flufenamic acid is a promising structural modification of well-known drug molecules. An effective approach in this field is micronization, employing "green" supercritical fluid technologies. This research raises some key questions to be answered on how to control polymorphic forms during the micronization of drug compounds. The results presented in this work demonstrate the ability of two-dimensional nuclear Overhauser effect spectroscopy to determine conformational preferences of small molecular weight drug compounds in solutions and fluids, which can be used to predict the polymorphic form during the micronization. Quantitative analysis was carried out to identify the conformational preferences of flufenamic acid molecules in dimethyl sulfoxide-d6 medium at 25 °C and 0.1 MPa, and in mixed solvent medium containing supercritical carbon dioxide at 45 °C and 9 MPa. The data presented allows predictions of the flufenamic acid conformational preferences of poorly soluble drug compounds to obtain new micronized forms.

Red Disperse Azo Dye Side Chains Influence on Polyethylene Terephthalate Dyeing Performances in Supercritical Carbon Dioxide Media.

Supercritical carbon dioxide dyeing (SDD) as a dyeing media not only provides a friendly dyeing environment but also significantly increases polymeric dyeing performances ascribed to strong azo dye affinity. Disperse azo dyes have shown to be highly efficient dyeing agents due to their facile coupling synthesis, side chains position, and length tunability to optimize absorption properties. Herein, we first synthesize two series of disperse red azo dyes via a coupling chemical route. Further, we investigate the position of the electron withdrawing group and alkyl chains length impact onto the absorption and color fastness properties. Upon synthesis, 1H NMR and mass spectroscopy were used to characterize our newly synthesized series dye structure. Also, according to spectroscopic characterization, the functional group positions as well as the alkyl chains length have a major impact on the dye series maximum light absorption wavelength and performance. We have performed SDD dyeing of polyethylene terephthalate woven and determined each dye color fastness, we find that a reduced electron withdrawing effect and alkyl chains increase reduce color-fastness performances. Overall, our dyes exhibited a good resistance against detergent water, perspiration, abrasion, and friction.

Formation of Metal–Hypercrosslinked Polystyrene Composites in a Supercritical Carbon Dioxide Medium and Their Catalytic Properties in the Hydrogenation of Diphenylacetylene

Formation of Metal–Hypercrosslinked Polystyrene Composites in a Supercritical Carbon Dioxide Medium and Their Catalytic Properties in the Hydrogenation of Diphenylacetylene

Pressure effect on lidocaine conformational equilibria in scCO2: A study by 2D NOESY

The work reports the results of an analysis of the lidocaine molecule conformational behavior in a supercritical carbon dioxide medium. Based on the nuclear Overhauser effect spectroscopy (2D NOESY) data, the authors determine the fractions of lidocaine molecule conformers in scCO2 at temperatures and pressures exceeding the critical point (308.15 K; 10–20 MPa). The paper also shows the effect of conformational inversion for this system at 308.15 K and 22 MPa. Since lidocaine polymorphic transformations can be accompanied by changes in the molecule conformation in the crystal elemental unit cell, it is quite urgent to determine the conformer fractions of this compound.

Features of Luminescent Properties of Alginate Aerogels with Rare Earth Elements as Photoactive Cross-Linking Agents.

Luminescent aerogels based on sodium alginate cross-linked with ions of rare earth elements (Eu3+, Tb3+, Sm3+) and containing phenanthroline, thenoyltrifluoroacetone, dibenzoylmethane, and acetylacetone as ligands introduced into the matrix during the impregnation of alginate aerogels (AEG), were obtained for the first time in a supercritical carbon dioxide medium. The impregnation method used made it possible to introduce organically soluble sensitizing ligands into polysaccharide matrices over the entire thickness of the sample while maintaining the porous structure of the aerogel. It is shown that the pore size and their specific area are 150 nm and 270 m2/g, respectively. Moreover, metal ions with content of about 23 wt.%, acting as cross-linking agents, are uniformly distributed over the thickness of the sample. In addition, the effect of sensitizing ligands on the luminescence intensity of cross-linked aerogel matrices is considered. The interaction in the resulting metal/ligand systems is unique for each pair, which is confirmed by the detection of broad bands with individual positions in the luminescence excitation spectra of photoactive aerogels.

Devulcanization of natural rubber/styrene-butadiene rubber unfilled blend in supercritical carbon dioxide using Tulbaghia violacea crude extract

A non-toxic and readily available potential devulcanizing agent, viz. Tulbaghia violacea Harv. plant bulbs crude extract , was used for the first time to non-isothermally devulcanize an unfilled natural rubber/styrene butadiene rubber blend in supercritical carbon dioxide medium. Temperature set-point and pressure were kept at 120 °C and 8 MPa, respectively, while the amount of extract and reaction time were optimized. Based on simultaneous optimization of the amount of extract and the initial time of devulcanization, the reactivity of the organo-sulphur compounds in an extract with the vulcanizate is seemingly dependent on the reaction time and temperature. Though organo-sulphur compounds in the plant bulbs crude extract had a significant effect on the vulcanizate, heat alone also caused chemical bonds breakage . Treatment with plant bulbs crude extract decreased the crosslink density while increasing both the sol fraction % and percent devulcanization to 45% and 75%, respectively, when devulcanization was performed for 6–17 min. Organo-sulphur compounds in plant bulbs crude extract had no effect when the reaction time was 18 min or more. Swelling tests, as well as gel permeation chromatography , Fourier-transform infrared spectroscopy and thermogravimetric analyses, on extract-treated and untreated vulcanizate suggested that the Tulbaghia violacea plant bulbs crude extract has the potential of producing improved-quality recovered rubber.

Hybrid materials based on inorganic aerogel and organic luminophore

A new luminescent hybrid material based on inorganic aerogel “LightSil” (hereinafter referred to as HM-LS) has been fabricated. Organic phosphor has been directly synthesized from boron and 8-hydroxyquinolinol within the aerogel porous structure during its supercritical drying. Intercalation of various amounts of boron ions (0.01, 0.05 and 0.1 wt%) proceed at the gel aging stage. Synthesis and supercritical drying of materials were conducted in high pressure apparatus in a supercritical carbon dioxide medium at 120 bar pressure, 40°C and 500 g/h gas flow rate. The influence of ion amount on the luminescent, physical and structural characteristics of HM-LS were investigated. Analysis of the PL spectra showed that HM-LS with a boron ion concentration of 0.05 wt% has a highest photoluminescence intensity at a wavelength of 513 nm.

UV‐Induced C−H Functionalization of Alkanes with NO2 in Supercritical Carbon Dioxide

AbstractA novel catalyst‐free method for functionalization of unbranched alkanes via radical nitration with UV‐activated nitrogen oxide (IV) in supercritical carbon dioxide medium has been developed. The method allows to transform these inactive substrates into corresponding nitrates and nitro compounds with outstanding yields (up to 65 %), using available reagents (NO2, O2) under mild reaction conditions (35–50 °C), and exhibits lower hazards compared to conventional analogues. An improved selectivity towards the nitrates has been achieved by adding pure oxygen to the reaction. Based on changes in reaction rate and product composition, the plausible reaction mechanism for the UV‐induced C−H functionalization of alkanes with nitrogen oxide (IV) and pure oxygen has been proposed.

Knoevenagel condensation reaction in supercritical carbon dioxide medium using a Zn(II) coordination polymer as catalyst

The replacement of conventional organic solvents by the so-called “green solvents” is a usual approach to more sustainable chemical processes. Supercritical carbon dioxide (scCO2) has been successfully regarded as a candidate for such a purpose. Moreover, it possesses moderate critical pressure and temperature conditions and may be easily separated from the catalytic system by a simple depressurization. In the present work, the new Zn(II) coordination polymer [Zn(L1)(NMeF)]n·n(NMeF) (Zn-CP 1) is reported, being prepared by the solvothermal reaction of 5-{(pyren-4-ylmethyl)amino}isophthalic acid (H2L1) with Zn(NO3)2·6H2O in N-methylformamide (NMeF). The SCXRD analysis revealed that Zn-CP 1 has a 1D double chain type of structure. Its potential as catalyst was studied in the Knoevenagel condensation of benzaldehyde and malononitrile as a model reaction under mild conditions, in scCO2 medium. An increasing trend was observed in the reaction yield as we moved from aprotic (THF) to protic (EtOH and H2O) polar co-solvents, reaching the full conversion in the case of water. It was found that scCO2, in the absence of a protic co-solvent, is not the most suitable medium for this reaction. The catalyst can be recycled without a considerable loss of activity; SEM, PXRD, FT-IR and TGA analyses indicate its high stability throughout the process.

Supercritical carbon dioxide assisted formation of crystalline materials for various energetic applications

This highlight gives an overview of recent advances in production of crystalline materials for high energy density applications for rechargeable batteries and solar cells or energetic compounds in supercritical carbon dioxide medium.