Production of alumino-borosilicate foamed glass body from waste LCD glass

A foaming process for waste LCD glass is presented, in which waste LCD glass is recycled to produce alumino-borosilicate foamed glass, which can eventually be used as a heat-insulating material, a light-weight aggregate for civil engineering applications, or a carrier for sewage treatment. The effects on waste LCD glass foaming of a variety of carbon foaming agents, metal salt foaming agents, and bonding agents are examined, as well as other factors such as chemical composition, foaming temperature, and grain size of the raw materials from the waste LCD glass. After examining all the variables that influence the foaming process, it was confirmed that the waste LCD glass is suitable as a raw material for producing alumino-borosilicate foamed glass. The alumino-borosilicate foamed glass has excellent physical properties, with density less than 0.14 g/cm³, heat conductivity less than 0.054 W/(mK) @20 °C, bending strength more than 35 N/cm², compressive strength more than 39 N/cm² and a coefficient of linear thermal expansion less than 4.5 × 10^?6 m/m °C. This clearly shows that the lightweight alumino-borosilicate foamed glass could be useful for various applications.     

Preparation of spherical foamed body with function of media for waste water treatment by using waste LCD glass

Using waste LCD glass as a base material helped developed the manufacturing process of the spherical foamed body and its varied functionality. Also, the manufactured spherical foamed body showed great performance as a water treatment media. By mixing 90 wt% of waste LCD glass, 100 parts by weight of glass mixture that has 10 wt% kaolinite as a shaping agent, 1.0 part by weight of carbon foaming agent, and mixture of each 1.5 parts by weight of Na₂CO₃, CaCO₃ and Na₂SO₄ as foaming agents and the MgO as a parting agent for 10 min of foaming calcination in the rotary kiln at 970–1000 °C, the spherical foamed body can be manufactured effectively. The manufactured spherical foamed body performed as a great water treatment media by showing 70.5% of SS removal efficiency, 56.1% of BOD removal efficiency, 57.5% of COD removal efficiency, 28.6% of denitrification and 49.8% of phosphorous removal.     

Polycarbonate foams with tailor-made cellular structures by controlling the dissolution temperature in a two-step supercritical carbon dioxide foaming process

Closed-cell polycarbonate foams were prepared using a two-step foaming process, which consisted of the initial dissolution of supercritical CO₂ (scCO₂) into PC foaming precursors and their later expansion by heating using a double contact restriction method. The effects of the parameters of both CO₂ dissolution and heating stages on the cellular structure characteristics as well as on the physical aging of PC in the obtained foams were investigated. A higher amount of CO₂ was dissolved in PC with increasing the dissolution temperature from 80 to 100 °C, with similar CO₂ desorption trends and diffusion coefficients being found for both conditions. PC foams displayed an isotropic-like microcellular structure at a dissolution temperature of 80 °C. It was shown that it is possible to reduce their density while keeping their microcellular structure with increasing the heating time. On contrary, when dissolving CO₂ at 100 °C and later expanding, PC foams presented a cellular morphology with bigger cells and with an increasingly higher cell elongation in the vertical growth direction with increasing the heating time. Comparatively, PC foams obtained by dissolving CO₂ at 100 °C presented a more marked physical aging after CO₂ dissolution and foaming, although this effect could be reduced and ultimately suppressed with increasing the heating time.     

Foaming of linear isotactic polypropylene based on its non-isothermal crystallization behaviors under compressed CO2

The non-isothermal crystallization behaviors of isotactic polypropylene (iPP) under ambient N₂ and compressed CO₂ (5–50 bar) at cooling rates of 0.2–5.0 °C/min were carefully studied using high-pressure differential scanning calorimeter. The presence of compressed CO₂ had strong plasticization effect on the iPP matrix and retarded the formation of critical size nuclei, which effectively postponed the crystallization peak to lower temperature region. On the basis of these findings, a new foaming strategy was utilized to fabricate iPP foams using the ordinary unmodified linear iPP with supercritical CO₂ as the foaming agent. The foaming temperature range of this strategy was determined to be as wide as 40 °C and the upper and lower temperature limits were 155 and 105 °C, which were determined by the melt strength and crystallization temperature of the iPP specimen under supercritical CO₂, respectively. Due to the acute depression of CO₂ solubility in the iPP matrix during the foaming process, the iPP foams with the bi-modal cell structure were fabricated.     

Fractionated extraction of saponins from Brazilian ginseng by sequential process using supercritical CO2, ethanol and water

Saponins are surfactants that reduce the surface tension of aqueous solutions, besides having pharmacological actions. In order to extract and fractionate saponins from Pfaffia glomerata roots and Hebanthe eriantha roots using supercritical technology, fractionated extracts were obtained from a sequential process in fixed bed using supercritical CO₂ (scCO₂), ethanol, and water as solvents. All extractions were carried out in four sequential steps, at 50 °C and 300 bar. In the first step, pure scCO₂ was used as solvent, while (a) scCO₂/etanol (70:30, w/w); (b) ethanol, and (c) ethanol/water (70:30, v/v) were used as solvents in the three subsequent steps. The extracts were analyzed by thin layer chromatography (TLC) and surface tension. The extraction yields of the four steps were 0.16, 0.55, 1.00, and 6.90% for P. glomerata roots, and 0.17, 0.58, 0.89, and 28% for H. eriantha roots, showing a predominance of high polarity compounds in these species. TLC analysis showed that the extraction process was selective according to the polarity of the solvent, and provided extracts containing different saponins, except for scCO₂ extraction. The extracts from the extraction using ethanol + scCO₂ (Step 2) showed the greatest ability to reduce the surface tension of water from 72 mN m⁻¹ (pure water) to 25 mN m⁻¹, suggesting that this step was the best for extraction of less polar saponins in the extracts. The critical micelle concentration (CMC) values were approximately 2 and 8 g L⁻¹ for P. glomerata and H. Eriantha, respectively. These results confirmed the efficacy of the extraction process under study.     

Kinetics of N-isopropylacrylamide polymerizations in supercritical carbon dioxide fluids

Free-radical polymerization kinetics of N-isopropylacrylamide (NIPAAm) using 2,2′-azobis(isobutyronitrile) (AIBN) as an initiator in supercritical carbon dioxide (scCO₂) was investigated. A high-pressure differential scanning calorimeter revealed that the melting temperatures of NIPAAm and AIBN were both decreased with increasing CO₂ pressure in a linear fashion and the polymerization could occur in CO₂ at 55 °C. The polymerization kinetics of NIPAAm in scCO₂ was compared with that in methanol (MeOH). At 55 °C, the induction periods of polymerizations in scCO₂ of 27.6 MPa were much longer (up to 6 h) than those in MeOH (about 30 min) for similar feed concentrations. The monomer conversions reached and molecular weights produced were much higher in scCO₂ than in MeOH. The reaction orders for initial monomer and initiator concentrations, [NIPAAm]₀ and [AIBN]₀, in initial stage of polymerizations were respectively 1.48 and 0.79 in scCO₂ and 1.27 and 0.51 in MeOH.     

Environmentally benign supercritical CO2 extraction of galanthamine from floricultural crop waste of Narcissus pseudonarcissus

The influence of diverse factors on the supercritical fluid extraction (SFE) with supercritical CO₂ (scCO₂) of galanthamine from bulbs of Narcissus pseudonarcissus cv. Carlton was investigated. The parameters that were studied were CO₂ density (temperature and pressure), flow rate and plant material particle size and pre-treatment. The highest yield (303 μg/g) was achieved by extracting 53–1000 μm particle-size powdered dried bulb material moistened with NH₄OH (25%, v/v) at 70 °C, 220 bar (690 kg/m³) for 3 h. Other N. pseudonarcissus alkaloids such as O-methyllycorenine and haemanthamine were also obtained. N. pseudonarcissus alkaloids as free bases are highly soluble in CO₂ at a high pH as opposed to the slightly soluble salt form in which they are generally found in plants. Therefore, plant material pre-treatment with a base is an essential step for galanthamine extraction. Scanning electron microscope (SEM) results also revealed that the desorption of N. pseudonarcissus alkaloids from the plant material rather than the solubility of the alkaloids in the scCO₂ plays a major role in this scCO₂ extraction. This extraction method has a good potential for industrial application.     

Sequential extraction of bioactive compounds from Melia azedarach L. in fixed bed extractor using CO2, ethanol and water

Melia azedarach L. is a plant with wide use in folk medicine since it contains many bioactive compounds of interest. The present study aimed to extract bioactive compounds from M. azedarach fruits by a sequential process in fixed bed using various solvent mixtures. Extractions were performed at 50 °C and 300 bar in four sequential steps using supercritical CO₂ (scCO₂), scCO₂/ethanol, pure ethanol, and ethanol/water mixture as solvents, respectively. The efficacy of the extraction process was evaluated by extraction yield and kinetics, and analysis of extracts by: (1) thin layer chromatography (TLC), (2) phenolics content, (3) reduction of surface tension of water, (4) gas chromatography (GC–MS), (5) electrospray ionization mass spectrometry (ESI–MS) and (6) antiviral activity. The overall extraction yield reached 45% and TLC analysis showed extracts with different composition. extract obtained from CO₂/ethanol mixture (SCEE) exhibited the greatest ability to reduce surface tension of water from 72.4 mN m⁻¹ [1] of pure water to 26.9 mN m⁻¹ of an aqueous solution of 40 g L⁻¹. The highest phenolics contents were observed in both the hydroalcoholic extract and scCO₂/ethanolic extract. Volatile oils were not detected in the supercritical extracts by GC–MS. MS analyses identified the fatty acids: linoleic, palmitic and myristic acid in the supercritical extract (SCE), and the phenolics: caffeic acid and malic acid in the other extracts. In addition, SCE and SCEE extracts showed significant inhibition percentage against Herpes Simplex Virus Type 1. The extraction process proposed in the present study produced extracts with significant potential for application in food and pharmaceutical industries.     

The effect of ethyl-lactate and ethyl-acetate plasticizers on PCL and PCL–HA composites foamed with supercritical CO2

The present study reports foaming of polycaprolactone (PCL) and PCL nano- and micro-composites with dispersed hydroxyapatite (HA) particles by means of binary mixtures of supercritical CO₂ (scCO₂) and either ethyl lactate (EL) or ethyl acetate (EA) as plasticizer. The effect of the size and concentration of HA particles, as well as the effects of the plasticizer type and the incorporation route were investigated aiming to fabricate porous scaffolds with uniform morphology and controlled pore size distribution. For this purpose, foaming experiments were carried out by selecting two operating temperatures, 40 and 45 °C, and two soaking times, 1 and 17 h. Furthermore, a double step of depressurization was used to promote the development of a double-scale pore size structure in porous scaffolds useful for tissue engineering.The results of this study indicated that supercritical foaming of PCL and PCL–HA composites is enhanced when the selected operating temperature and time are 45 °C and 17 h, respectively. Furthermore, although both EL and EA plasticizers enhanced the low temperature foaming of the materials, we demonstrated that the route of incorporation of the plasticizer is a critical aspect for enhancing composite foaming and scaffold fabrication. From this point of view, the best results were achieved when EA was pre-mixed with the polymeric powder for preparing a dough for the foaming process.     

Selective hydrogenation of chloronitrobenzene to chloroaniline in supercritical carbon dioxide over Ni/TiO2: Significance of molecular interactions

The hydrogenation of chloronitrobenzene to chloroaniline was investigated over Ni/TiO₂ at 35 °C in supercritical CO₂ (scCO₂), ethanol, and n-hexane. The reaction rate followed the order of scCO₂ > n-hexane > ethanol. In scCO₂, the selectivity to chloroaniline and to aniline over Ni/TiO₂ were 97–99.5% and <1%, respectively, in the conversion range of 9–100%. The high chemoselectivity to chloroaniline cannot be achieved over Ni/TiO₂ in ethanol and n-hexane. In situ high-pressure Fourier transform infrared measurements were made to study the molecular interactions of CO₂ with the following reactant and reaction intermediates: chloronitrobenzene, chloronitrosobenzene, and N-chlorophenylhydroxylamine. The molecular interaction modifies the reactivity of each species and accordingly the reaction rate and the selectivity. The influence of Cl substituent on the interaction modes of CO₂ with these reacting species is discussed. Possible reaction pathways for the hydrogenation of chloronitrobenzene in scCO₂ over Ni/TiO₂ are also proposed.     

Supercritical CO2 generator using bubble collapse by water hammer

We have developed a new apparatus to dynamically generate supercritical CO₂ (scCO₂) bubbles in water using a water hammer facility by efficiently concentrating water energy. We measured the internal and external pressures of a CO₂ bubble covered with a rubber membrane using pressure transducers, and observed the bubble's oscillations by a high-speed video camera. We evaluated the maximum duration of the scCO₂ for conditions 60 μs in experiments. We performed numerical simulations using the Rayleigh–Plesset equation by substituting the experimental external pressure profiles of the bubble and confirmed that numerical results agreed with the experimental internal pressure. Moreover, in the minimum external pressure condition where we experimentally achieved the condition of scCO₂ in the bubble for 16 μs by water hammer, we obtained the maximum duration of scCO₂ conditions up to 55 μs by numerical simulations assuming isotropic compression.     

Preparation and characterization of polystyrene foams from limonene solutions

The foaming process has been traditionally performed at high temperature because the CO₂ and the polymer should behave as a homogeneous solution. The addition of a solvent could avoid the high working temperature while the homogeneity is ensured. Among the terpene oils, limonene outlines as a good candidate to carry out the dissolution of polystyrene because it respects the green chemistry principle, it is highly soluble in CO₂ and very compatible with the polymer.The sorption of CO₂ is the first step of the foaming process. The presence of the terpene oil enhances the solubility of the gas which is solubilized in the Polystyrene as well as in the limonene. During the foaming process, many parameters can be tuned to customize the foams. In this work, a fractional factorial design of experiment was proposed to determine the effect of pressure, temperature, concentration of the solution, contact time and vent time over the diameter of cells, its standard deviation and the cells density. The proposed foaming process can be simply performed at mild pressure and temperature thanks to the presence of the solvent. The results showed that the most suitable conditions to foam polystyrene from limonene solutions are 90 bar, 30 °C, 0.1 gPS/ml Lim, 240 min contacting and 30 min venting. Finally, the samples were characterized to determine the amount of residual solvent, their glass transition and degradation temperature checking that the foams presented around 5% of solvent traces but did not show any evidence of degradation.     

Silicon carbide-based foams derived from foamed SiC-filled phenolic resin by reactive infiltration of silicon

Macro-cellular porous silicon carbide-based foams were fabricated by reactive infiltration of melt silicon into porous carbonaceous preforms pyrolyzed from foamed SiC-filled phenolic resins (PF). The SiC-filled PF foams were prepared at 80 °C with different heating rate. The effect of heating rate on the foaming behavior of the liquid SiC-filled PF mixture and the microstructure of the foams were investigated. The foamed SiC-filled PF was then pyrolyzed at 1000 °C and infiltrated by melt Si at 1600 °C, leading to the formation of open macro-cellular structure. At a heating rate of 6 °C min⁻¹, Si-infiltrated foams with a porosity of ~72% and a mean pore size of ~0.5 mm were obtained. The Si-infiltrated foams with dense struts mainly inherited the pore structure of pyrolyzed preforms. The main phases of SiC-based foams were α-SiC, β-SiC and the remnant Si, which contributed to high compressive strength of the SiC-based foams.     

Selective hydrogenation of citral with transition metal complexes in supercritical carbon dioxide

The activity and selectivity of the transition metal complexes formed from Ru, Rh, Pd and Ni with triphenylphosphine (TPP) have been investigated for hydrogenation of citral in supercritical carbon dioxide (scCO₂). High activities are obtained with Ru/TPP and Pd/TPP catalysts, and the overall activity is in the order of Pd≈Ru > Rh > Ni. The Ru/TPP complex is highly selective to the formation of unsaturated alcohols of geraniol and nerol. In contrast, the Pd/TPP catalyst is more selective to partially saturated aldehydes of citronellal. Furthermore, the influence of several parameters such as CO₂ and H₂ pressures, N₂ pressure and reaction time has been discussed. CO₂ pressure has a significant impact on the product distribution, and the selectivity for geraniol and nerol can be enhanced from 27% to 75% with increasing CO₂ pressure from 6 to 16 MPa, while the selectivity for citronellol decreases from 70% to 20%. Striking changes in the conversion and product distribution in scCO₂ could be interpreted with variations in the phase behavior and the molecular interaction between CO₂ and the substrate in the gas phase and in the liquid phase.     

New data on arsenic sorption properties of Zn–Al sulphate layered double hydroxides: Influence of competition with other anions

The adequacy of synthetic Zn–Al-sulphate LDHs to remove arsenic from aqueous systems was tested through sorption experiments, using a series of aqueous solutions with dissolved HAsO₄^2 − together with other anions (Cl⁻, SO₄^2 −, MoO₄^2 −, HCO₃⁻, CO₃^2 −) to assess their competition influence on the As removing process. The competitors were added into the solution both simultaneously and afterwards with respect to HAsO₄^2 − in order to verify the effectiveness and the possible reversibility of the As sorption process. The results showed that only carbonates species, in particular in the fully deprotonated form CO₃^2 −, affect significantly the otherwise high efficacy of the sorption process. In fact, up to ~ 90% of HAsO₄^2 − can be removed from the solution, decreasing to ~ 60% in the presence of CO₃^2 −, whilst up to ~ 30% of HAsO₄^2 − can be desorbed when CO₃^2 − is added afterwards into the solution. Considering the very restricted range of pH where HAsO₄^2 − and CO₃^2 − are simultaneously the predominant species in the solution (~ 10 < pH < ~ 11.5), Zn–Al-sulphate LDHs could be successfully used for the treatment of As contaminated waters with pH ranging from circum-neutral to moderately alkaline.     

Tandem Staudinger-Aza-Wittig reaction in supercritical CO2: Synthesis of a pharmaceutical interest compound

The aim of this research was to investigate the capability of using supercritical CO₂ (scCO₂) as reagent and solvent in the synthesis of pharmaceutical cyclodextrinyl derivatives in smooth reaction conditions. In this way we have followed the kinetics of a synthesis which was previously realized in DMF, by using tandem Staudinger-Aza-Wittig (S.A.W.) reaction in scCO₂ at 200 bars pressure in a 100 mL reactor. The results show that the reaction in scCO₂ showed a second order kinetics with the yield of 92%.     

In situ quantification of minor compounds in pressurized carbon dioxide using Raman spectroscopy

In this work, we present an optical approach that allows quantification of compounds dissolved down to a sub 10 ppm (molar) level in supercritical carbon dioxide (scCO₂) by in situ Raman spectroscopy. The quantification strategy is based on the consideration of Raman signal intensity ratios and of weak Raman signals of CO₂. The first measure makes the quantification strategy independent of the refractive index, laser power fluctuations and changes in alignment, and is thus robust against variations of the operation conditions. The second measure circumvents the classical challenges related to the dynamic range limit of detectors, which is inherent to the quantification of minor compounds. Example solubilities of the wax alkyl ketene dimer (AKD) in CO₂ were quantified at 333 K and a range of pressures from 10 MPa to 18 MPa. The solubilities are between 0.1 mg g⁻¹ and 1.5 mg g⁻¹ corresponding to ∼9 ppm and ∼132 ppm (molar), respectively.     

Phase equilibria of palm oil,palm kernel oil,and oleic acid + supercritical carbon dioxide and modeling using Peng–Robinson EOS

Vapor–liquid equilibria of the binary supercritical carbon dioxide (scCO₂) + oleic acid, scCO₂ + palm oil, and scCO₂ + palm kernel oil were measured at a wide range of temperatures from 333.2 to 373.2 K and pressures from 8.5 to 35 MPa in a circulation-type phase equilibrium apparatus. The samples from liquid and vapor phases were analyzed using UV–vis spectrometer and a liquid hold-up equipment. The phase equilibrium data were correlated with Peng–Robinson Equation of State (PR-EOS) using Wong–Sandler mixing rule and optimum values of binary interaction parameters were determined. The relative deviation between experimental data and predicted data was in the range of 6.9–8.7%, suggesting that the PR-EOS with Wong–Sandler mixing rule is capable of predicting the vapor–liquid equilibria of oleic acid + scCO₂, palm oil + scCO₂, and palm kernel oil + scCO₂.     

Thermodynamics and regeneration studies of CO2 adsorption on multiwalled carbon nanotubes

Multiwalled carbon nanotubes (CNTs) were fabricated and modified by 3-aminopropyl-triethoxysilane (APTS) solutions to study thermodynamics and regeneration of CO₂ adsorption from gas streams. The CO₂ adsorption capacities of CNTs and CNT(APTS) decreased with temperature indicating the exothermic nature of adsorption process while the thermodynamic analysis gave low isosteric heats of adsorption, which are typical for physical adsorption. The cyclic CO₂ adsorption on CNT(APTS) showed that the adsorbed CO₂ could be effectively desorbed via thermal treatment at 120 °C for 25 min while the adsorbed CO₂ due to physical interaction could be effectively desorbed via vacuum suction at 0.145 atm for 30 min. If a combination of thermal and vacuum desorption was conducted at 120 °C and 0.145 atm, the time for effectively desorbing CO₂ could be further shortened to 5 min. The adsorption capacities and the physicochemical properties of CNT(APTS) were preserved during 20 cycles of adsorption and regeneration. These results suggest that the CNT(APTS) can be stably employed in prolonged cyclic operation and they are thus possibly cost-effective sorbents for CO₂ capture from flue gases.     

Fabrication of highly insulating foam glass made from CRT panel glass

We prepared low-density foam glasses from cathode-ray-tube panel glass using carbon and MnO₂ as the foaming agents. We investigated the influence of the carbon and MnO₂ concentrations, the glass-powder preparation and the foaming conditions on the density and homogeneity of the pore structure and the dependence of the thermal conductivity on the foam density. The results show that the moderate foaming effect of the carbon is greatly improved by the addition of MnO₂. A density as low as 131 kg m⁻³ can be achieved with fine glass powder. The foam density has a slight dependence on the carbon and MnO₂ concentrations, but it is mainly affected by the foaming temperature and the time. The thermal conductivity of the foam-glass samples is lower than that of commercial foam glasses with the same density. The lowest value was determined to be 42 mW m⁻¹ K⁻¹ for a foam glass with a density of 131 kg m⁻³. A further improvement in the closed porosity could potentially decrease the thermal conductivity even further, and thus our approach has great potential in terms of a thermal insulation material.