Journal of Supercritical Fluids最新文献

Supercritical carbon dioxide (SCCO₂) fracturing significantly enhances shale gas recovery, which is influenced by particle size. We soaked shale in SCCO₂ and investigated the impact of SCCO₂ on different particle sizes. Large-particle shales showed the largest percentage changes in specific surface area and total pore volume (54.11 %, 87.87 %; 58.59 %, 76.32 %) followed by small-particle size shales. This trend was also observed in other pore structure parameters. The particle-size effect is: Large-particle shale, with abundant microfractures, enhances SCCO₂ flow and pore alteration. Small-particle shale's high specific surface area facilitates SCCO₂ penetration. Medium-particle shale is less affected due to balanced interactions of these factors. Methane is primarily found in large and medium pores and microfractures. Methane adsorption in shale mainly involves multi-layer adsorption. Following SCCO₂ treatment, pore fractures narrowed, increasing the proportion of methane molecules adsorbed as a single-layer. This study is crucial for evaluating the fracturing effects on shale gas wells.

A supercritical CO₂ assisted process was used to perform a comparative study between liposomes and niosomes. Process operating conditions were fixed at 100 bar and 40 °C, and the produced vesicles were characterized in terms of mean diameter, size distribution, ζ-potential, and stability over time. Mean diameters of liposomes and niosomes were similar (130 ± 37 nm for liposomes and 141 ± 36 nm for niosomes) and both systems were stable after 1 month from production. Ascorbic acid (AA) was loaded in both kinds of formulation. AA encapsulation efficiency was equal to 92 % and 99 % for liposomes and niosomes, respectively, and DPPH-activity was larger than 90 % in both vesicular systems. Drug release tests revealed that AA was released in 120 min and 240 min from liposomes and niosomes, respectively, due to a different compactness of the vesicle bilayer.

We here report the first occurrence of a preferential cocrystallization process assisted by compressed carbon dioxide. Our study focuses on the Nefiracetam-Mandelic acid conglomerate forming system. The cocrystal conglomerate was successfully crystallized using compressed CO₂ as antisolvent, and acetone, ethyl acetate, or isobutanol as solvents for starting solutions in the so-called GAS process. We then focus on acetone to successfully perform preferential cocrystallization supported by compressed CO₂. A critical step in the design of the process is the adaptation of the set-up to allow the introduction of enantiopure seeding inside the reactor. Based on the use of seeded rings, we test several seeding configurations to enhance enantioseparation through the simultaneous crystallization of both enantiomers in two different areas of the reactor.

Arthrospira platensis polyphenolic natural extracts have several benefits for human health. Due to their instability and reduced shelf-life, these extracts are usually encapsulated. This work analyzed the supercritical emulsion extraction (SEE) process for the production of polymeric nanoparticles loaded with A. platensis polyphenolic extracts. The objective of this work was to evaluate a powdered encapsulation system to overcome the drawbacks of liquid systems, which are those mainly used for microalgae extract stabilization. An optimization study was performed investigating different process parameters and comparing the obtained particles in terms of particle size distribution, morphology, and encapsulation efficiency. The process permitted the successfull production of loaded polymeric nanoparticles with an encapsulation efficiency up to 74 % in the best operating conditions. The SEE process allowed a better control of morphology and particle size distribution of the nanometric particles operating in a continuous mode.

Supercritical water gasification (SCWG) and oxidation (SCWO) were promising technologies for treating municipal sludge; however, corrosion hindered their development. To obtain the candidate material for preheaters, corrosion characteristics of 316, 316 L, Incoloy 800, 825, and TA-10 were investigated at 350 °C and 400 °C. For SCWG and SCWO reactors, corrosion behaviors of 316, Incoloy 800, 825, Inconel 600, 625, and Hastelloy C276 were explored at 450 °C and 520 °C, with and without oxidants. Near the critical point of water, corrosion rates of all materials were below 0.4 mm·a⁻¹, with 316 L being the candidate material. According to the pH variation, materials underwent activation (350 °C) and passivation (400 °C) pathways. During SCWG and SCWO, Incoloy 825 and Inconel 625 were prioritized at 450 ℃ and 520 ℃, exhibiting corrosion rates below 0.40 mm·a⁻¹ and 0.50 mm·a⁻¹, respectively. Chemical corrosion dominated and double-layer oxide films (Fe₃O₄-FeCr₂O₄ and NiO-Cr₂O₃) formed.

Cubic equations of state (EoS) remain the most widely used models in chemical engineering, and their predictive capabilities are highly dependent on mixing rules (MR). Considered as one of the most accurate, Wong Sandler's (WS) MR, have been generalized in this work, to allow its use with all 2-parameter (PR, SRK, …) and 3-parameter (PT, mPT, NEOS, …) cubic EoSs. The procedure for implementing the generalized WS MR is presented and tested with PR, PT and its variants (mPT and NEOS) on vapor-liquid equilibrium (VLE) and density data on various classes of mixtures for different types of use (hydrogen, CCUS, refrigeration). The results clearly show the benefits of this type of MR, especially around the critical point and for density data without considering volume translation frequently used with PR and SRK EoS.

The emergence of expanded thermoplastic polyurethane foam beads (ETPU) has expanded the application range of polymer foam materials. However, most of the prepared bead foam products suffer from high shrinkage rate, high density, and poor interfacial bonding, severely affecting the mechanical stability and lightweighting of the products. Herein, this study constructed thermoplastic polyurethane/polybutylene succinate (TPU/PBS) bead blend foams with a segregated microcellular network structure (SMNS) for the first time, where the TPU/PBS continuous phase formed the SMNS and the bead phase was consisted of TPU foam beads. The results showed good interfacial bonding between the continuous and bead phases. By adding PBS to the continuous phase, the shrinkage percentage of TPU/PBS bead blend foam decreased from 79.19 % to 67.31 %, reduced by 15.0 %. In addition, the foam expansion ratio gradually decreased with increasing PBS content, dropping from 12.07 to 9.03. Moreover, TPU/PBS bead blend foams exhibited good energy absorption and mechanical stability without sacrificing thermal insulation performance. This work effectively reduced the shrinkage of TPU based foam materials, offering a simple and economical solution for the preparation of dimensionally stable, well-interfaced, and lightweight polymer foams.

Caryocar villosum (Aubl.) Pers. is a fruit native to the Amazon region, popularly known as piquiá. The supercritical extraction process of piquiá pulp was investigated in this work, considering the influence of temperature, pressure and solvent density on the extraction yield. The quality of the extract was evaluated in terms of fatty acid profile, functional quality indices, physicochemical characterization and α-tocopherol content. The extraction yield resulted to be greater with increasing pressure in each isotherm. The highest extraction yield was 62.74 %, while the lowest was 44.01 %. The main fatty acids observed in the extracts obtained under all operating conditions were oleic and palmitic. The results indicated that piquiá extract obtained via supercritical CO₂ presents itself as a potential product to be explored for applications in the food, cosmetic and pharmaceutical industries due to its composition and functional quality.

The production of biopolymeric aerogels, for tissue engineering, currently involves three steps: gelation (hydrogel), solvent exchange (alcogel), and supercritical drying (aerogel). The alcogel formation, the longest step, can be optimised by exploring high pressures/mild temperatures. This work aimed to integrate/optimise the production process of alginate/gelatine aerogels, by performing solvent exchange and drying continuously within the same equipment. High-pressure solvent exchange (HPSE) was compared with the conventional method by analysing the alcogel and solvent with two complementary analytical techniques: Differential Scanning Calorimetry (DSC) and Refractive Index (RI). HPSE resulted in a faster solvent exchange, reducing 86 % of the processing time. The solvent exchange conditions did not significantly affect the aerogel structure, density, porosity, and surface area. Still, HPSE and the drying time influenced pore distribution and decreased mechanical properties. The drying stage was optimised to 2 h, showing the feasibility of integrating solvent exchange and supercritical drying for alginate-gelatine aerogels production.