Adsorption of carbon dioxide on ionic liquids-modified active carbons and amino-modified polymer

Active carbons with various particle sizes (38–150, 300–500 and 800–1,200 μm) were modified by ionic liquids (ILs), and organic polymer was modified by acrylamide using a simple procedure, and these materials were applied to capture carbon dioxide (CO₂). The CO₂ adsorption amounts were calculated using a mass balance equation at three different temperatures (298.15, 308.15 and 318.15 K), respectively, and the influences of gas pressure, particle size and temperature on adsorption were discussed. Experimental results showed that the CO₂ adsorption capacity of ILs-modified active carbons was better than amino-modified polymer, and the smaller particle size (38–150 μm) ILsmodified active carbons had the largest adsorption capacity at 298.15 K. Compared with previous research about polyethyleneimine (PEI)-modified silica gel, the adsorption amount of CO₂ on ILs-modified active carbons has been greatly improved with lower cost.     

Synthesis and characterization of nanocomposite MCM-48-PEHA-DEA and its application as CO2 adsorbent

Three nanocomposites containing MCM-48-35PEHA-15DEA (35 and 15 as weight percent of amine addition), MCM-48-30PEHA-20DEA and MCM-48-25PEHA-25DEA of mesoporous silica MCM-48 modified by the mixture of pentaethylenehexamine (PEHA) and diethanolamine (DEA) have been synthesized and used to study the adsorption of carbon dioxide (CO₂). They are characterized by low angle x-ray diffraction (XRD), Fourier transform infrared (FT-IR) and Brunauer-Emmet-Teller (BET) analysis. MCM-48-35PEHA-15DEA (as optimized adsorbent) shows CO₂ adsorption capacity of 0.51 (m·mol CO₂/g-adsorbent) at 1 bar and 298 K, much higher than CO₂ adsorption capacity on polyethyleneimine, pyrrolidinepropyl and polymerized aminopropyl loaded MCM-48.     

α-Amylase immobilization capacities of mesoporous silicas with different morphologies and surface properties

α-Amylase was encapsulated in several mesoporous materials (folded sheet mesoporous silica (FSM), cubic mesoporous silica (KIT-6), and two-dimensional hexagonal mesoporous silica (SBA-15)) that differed morphologically in terms of particle shape, pore size, and pore structure. The encapsulation capacity and thermal stability of encapsulated α-amylase were examined. The amount of α-amylase encapsulated increased with increasing pore size in the following order: SBA-15 < KIT-6 < FSM. Nitrogen adsorption experiments were performed before and after α-amylase encapsulation in mesoporous silicas with pore sizes larger than the size of α-amylase, confirming that α-amylase was encapsulated in the pores. Among mesoporous silicas with similar pore sizes, FSM was found to have the highest capacity for α-amylase encapsulation both per weight and per surface area of silica. Furthermore, α-amylase encapsulated in FSM demonstrated high thermal stability at 90 °C relative to the thermal stability of free α-amylase or free α-amylase encapsulated in other mesoporous silicas. Zeta potential measurements showed that the FSM surface had an isoelectric point that was lower than that of other mesoporous silicas, and hydrophilicity measurements showed that its surface was more hydrophilic. The surface properties of FSM contributed to the high thermal stability of the α-amylase encapsulated within the pores.     

Recrystallization of tetracycline hydrochloride using supercritical anti-solvent process

Tetracycline hydrochloride (TTC) was micronized by an Aerosol Solvent Extraction System (ASES) using supercritical CO₂. The effects of solvent, pressure and temperature of CO₂, solution concentration, and solution feed rate on particle size were investigated. Mean particle sizes of processed TTC were 0.16–0.31 μm, but the morphologies of processed particles were affected by agglomeration between the primary particles. Mean particle sizes of unprocessed TTC were ca. 200 μm and the shapes were irregular with rough surfaces. Especially, particle sizes increased from 0.18 to 0.31 μm as CO₂ temperature increased. In addition, particle sizes increased from 0.18 to 0.23 μm as TTC concentration increased. Powder X-Ray diffractometry revealed that processed particles were amorphous whereas unprocessed particles showed strong crystallinity.     

Adsorption equilibria of benzoic acid on silica gel from supercritical carbon dioxide

Supercritical fluids, especially carbon dioxide, are increasingly used as carriers for adsorption-desorption processes, particularly in the pharmaceutical industry. Nevertheless, equilibria data for such processes are rather limited. Therefore, in this work, the adsorption equilibria of benzoic acid onto non-modified silica gel from scCO₂ were evaluated by Supercritical Fluid Chromatography applying the Peak Maxima method. Solubility of benzoic acid in scCO₂ was enhanced by addition of 2-propanol.The effects of modifier content, temperature and pressure on the solute loading were investigated. Experimental data were best described by the cubic Hill isotherm model, which accounted for the change of curvature of the elution profiles observed as concentrations in the mobile phase increased. For the concentration range reached in this study (up to 6 mg/mL), adsorption of benzoic acid was favoured at low modifier contents, high temperatures and low pressures, conditions at which the solvating power of the modified scCO₂ decreased.     

Use of novel polyetheralkanolamine comb polymers as pigment dispersants for aqueous coating systems

The adsorption of a series of polyetheralkanolamine comb polymers characterized by a different length of the hydrophilic tail has been investigated at the carbon black/water interface by measuring adsorption isotherm, contact angle, wetting rate, zeta potential, and particle size distribution. Zeta potential measurements and adsorption layer thickness results suggest that polyetheralkanolamines with high ethylene oxide (EO) content provide only steric stabilization and they adsorb at the interface with the ethylene oxide chains in a coil conformation. The thickness of the adsorbed layer increases with increasing EO units; however, the surface tension and interfacial tension decrease with increasing EO content. Adsorption isotherms show that most of the added polyetheralkanolamine adsorbs onto the carbon black and only a small amount stays in the water phase. When treated with a polyetheralkanolamine, carbon black dispersions show uniform (unimodal) and narrow particle size distribution with very small median sizes of about 0.10 μm. The pigment concentrates containing the polyetheralkanolamine show excellent color compatibility in various decorative commercial white paints containing a wide range of resins and exhibit low viscosity with nearly Newtonian flow behavior. Presented at the 2006 FutureCoat! Conference, sponsored by the Federation of Societies for Coatings Technology, in New Orleans, LA, on November 1–3, 2006.     

Grain size composition and porous structure of carbon hearth block materials for aluminum electrolyzers

Results are provided for the design of a carbon refractory structure with a pore size of less than 25 μm. It is established that if in planning the charge for carbon blocks the coarse fraction (10 – 5 mm) is excluded, converting the medium and fine fractions to 100%, then the sizes of fractions become close to those calculated by equations used traditionally describing optimum particle packing. In a three-fraction charge carbon material compositions composites are obtained within which the predominant pore size is less than 25 or even 10 mm.     

硅胶粒径对太阳能吸附制冷系统性能的影响

针对以硅胶-水为工质对的太阳能吸附式制冷系统,实验研究了不同粒径的硅胶材料对吸附床传热传质特性及系统制冷能力的影响。三组对比实验的硅胶材料平均粒径分别为1mm、3mm和5mm,在太阳辐射接近的条件下完成实验测试,结果表明粒径中等的硅胶材料表现最优,其制冷系数COP和按照循环周期定义的比制冷功率SCP2均最高。小粒径材料虽然使吸附剂填充量有所增加,但是会导致吸附床轴向传质阻力增加,影响其末端吸附能力的发挥。而材料的粒径过大,则会降低吸附床的吸附剂填充量及其传热性能,从而导致预热脱附和冷却过程的时间延长,不利于系统的制冷性能改善。实验结果表明,吸附剂粒径是影响太阳能吸附式制冷系统工作性能的一个重要因素,在系统设计中需要给予重视。     

Synthesis of an affinity adsorbent based on silica gel and its application in endotoxin removal

An affinity media for endotoxin removal based on silica gel was prepared by activation with silane coupling agent and subsequent conjugation with histidine (His) as a ligand. The influence of pore size and particle dimension of the silica gel and the grafting conditions such as reaction temperature and concentration of His in solution on the grafting yield of His were studied by means of IR, thermogravimetric analysis and elemental analysis. The results show that the silica gel with a particle size of 200 μm and a pore size of about 12 nm was a good carrier material for the preparation of the affinity adsorbent. Under the optimal conditions, histidine was covalently immobilized on silica gel at about 20 mg/g, with a corresponding maximum endotoxin adsorption capacity q_m in contaminated water of about 1.2 mg/g and an apparent dissociation constant K_d of about 1350 μg/L. The adsorbent had little nonspecific adsorption from a protein-containing solution.     

Computer simulation for storage of methane and capture of carbon dioxide in carbon nanoscrolls by expansion of interlayer spacing

We perform a molecular simulation study on methane and carbon dioxide storage in carbon nanoscrolls. The effects of temperature and pressure, interlayer spacing, VDW gap and innermost radius on the gas storage have been examined extensively. It is found that the adsorption of gases on pristine carbon nanoscrolls is relatively low. However, once the interlayer spacing is expanded, both adsorption capacities of methane and carbon dioxide exhibit a significant improvement. In particular, the excess uptake of methane reaches 13 mmol/g at p = 6.0 MPa and T = 298.15 K and VDW gap Δ = 1.1 nm, which is about 3.5 times of uptake of the pristine carbon nanoscrolls; while the uptake of carbon dioxide could also be raised by 294.9% at T = 298.15 K and p = 3.0 MPa and Δ = 1.5 nm, reaching 30.21 mmol/g at 6.0 MPa. This work demonstrates that carbon nanoscrolls with an expansion of interlayer spacing may be a suitable material for methane storage and carbon dioxide capture.     

Photocatalytic degradation of methanol on titania and titania–silica aerogels prepared by non-alkoxide sol–gel route

Titania and titania–silica aerogels were prepared by alkoxide or non-alkoxide sol–gel route and subsequent supercritical drying with carbon dioxide at low temperature. The resulting aerogels having high surface area and mesoporosity were used as photocatalysts for gas phase methanol degradation reaction. Photocatalytic degradation reactions were carried out on titania and titania–silica aerogels, and commercial Degussa P-25 titania. The photocatalytic activities of titania and titania–silica aerogels were higher than that of the P-25. While the conversion of methanol degradation over the P-25 catalyst was only 50–60%, that for the titania aerogel was observed to be above 98% due to the higher specific surface area and the well developed mesoporous structure. In spite of lower titania contents, much higher surface area and high dispersion of titania of titania–silica aerogel gave rise to the high photocatalytic activity in comparison to those of titania aerogels. Moreover, titania–silica aerogel was also used for the photodegradation and adsorption hybrid system. It was observed that the high removal efficiency for methanol was caused by the combination of higher catalytic activity and adsorption capacity.     

Synthesis of mesoporous silica from bottom ash and its application for CO<Subscript>2</Subscript> sorption

A supernatant solution of silicate species extracted from bottom ash in a power plant was used to prepare a mesoporous silica by the synthesis protocol of SBA-15. XRD, N₂ adsorption-desorption, and TEM confirmed a disordered mesopore structure. The pore volume and average pore size of the product were significantly larger than SBA-15 prepared using pure chemicals, and complementary textural mesoporosity was detected. When the mesoporous silica was tested for carbon dioxide sorption after polyethyleneimine (PEI) impregnation, substantially higher CO₂ sorption capacity (169 mg CO₂/g-sorbent) was achieved than that of PEI-impregnated pure SBA-15 under the same test conditions. High CO₂ sorption capacity was maintained when the gas composition was changed to 15% CO₂, and the hybrid material exhibited satisfactory performances during the 10 recycle runs.     

Synthesis of hard mesoporous macro-spheres with silicate and aluminosilicate compositions

This study reports the synthesis mechanism and the influence of different variables in the preparation of mesoporous macro-spheres having silicate and aluminosilicate compositions. The spheres possess sizes in the range 200–1000 μm with a narrow particle size distribution and a significant mechanical resistance (hard macro-spheres). In addition, the presence of a highly regular mesoporosity (around 3 nm) and of a high surface area (normally about 1000 m²/g) make these materials as very interesting self-supported adsorbents or catalysts that could be directly applied without no binder, which is a great advantage compared to materials in powder form. The synthesis of the hard mesoporous spheres takes place in a biphasic system, generated by the use of tetrabutoxysilane as silica source, which is reacted with water and NaOH leading to the formation of small primary particles which initially do not present any mesoscopic ordering. However, after about 5 h of synthesis, the presence of cetyltrimethylammonium chloride, as surfactant, gives rise to the detection of a mesostructured silica material. Subsequently, after 9 h of synthesis the small mesostructured particles, with sizes in the micrometer range, acquire a spherical shape. Finally, the reorganization and fusion of these particles cause the formation of the silica macrospheres, with a particle size of several hundreds of micrometers. When the synthesis is carried in the presence of an aluminium source, the aluminosilicate materials so obtained exhibit smaller surface area and pore volume and greater particle size than the pure silica ones.     

Structural, optical, thermo-mechanical and transport properties of ion irradiated polymer membranes

Summary The modifications in PET induced by swift heavy ion irradiation are analyzed. PET membrane of 15 μm was irradiated by Cl⁹⁺ ions of 100 MeV at TIFR Mumbai. The changes due to exposure to high-energy ions were investigated by Fourier Transform Infrared (FTIR) and Ultraviolet/ Visible absorption (UV/VIS) spectroscopies, X-Ray diffraction technique, dynamic mechanical analysis and by the gas permeation. A significant loss of crystallinity is observed by the XRD data. Particle size or grain size calculated using Scherrer formula indicates measurable change in particle size of irradiated samples. The polymer chain scissions and structure degradations are expected to occur for irradiated samples. Optical properties of the films were changed due to irradiation that could be clearly seen in the absorption and FTIR spectra. Gas permeation through these membranes before and after irradiation using hydrogen and carbon dioxide gases shows that permeability for both gases increased after irradiation but permeability for hydrogen is higher than carbon dioxide due to its small molecular size.     

Microstructure and reactivity evolution of colloidal silica binder in different systems at elevated temperatures

Colloidal silica as nanostructured binder for refractory castables has attracted many attentions in recent years. In the present study, phase composition, microstructure and reactivity evolution of silica gel at different heating conditions were investigated to find suitable system for colloidal silica application. The results showed that atmosphere and carbon slightly affected phase composition of the silica gel at elevated temperatures, and the crystalline phases were composed of major α-cristobalite and minor α-tridymite. The morphology and particle size of the silica gel were greatly affected by atmosphere and carbon during heating. The spherical nano-silica particles with sizes of 40–50 nm rapidly grew into macroscale rod-like particles with temperature increasing from 800-1000 °C to above 1200 °C in air, and sintering of silica particles was observed. However, the size and morphology of the spherical nano-silica particles retained at high temperature in a reducing atmosphere, and many well developed columnar mullite crystals and some SiC whiskers formed on heating silica gel, alumina fines and carbon at 1500 °C, which was due to carbon inclusions retarding the growth of nano-silica particles and the nano silica remained high reactivity at high temperature. Thus, colloidal silica was suitable for application in carbon-containing refractory castables.     

Synthesis of mesoporous materials SBA-15 and CMK-3 from fly ash and their application for CO2 adsorption

A supernatant solution of silicate species extracted from coal fly ash in a power plant by alkali fusion was used in acidic condition to prepare a mesoporous silica SBA-15. The SBA-15 was used as a template for the synthesis of a mesoporous carbon CMK-3 using sucrose as a carbon source. Characterization of the produced mesoporous materials by XRD, N₂ adsorption-desorption, SEM, and TEM confirmed the formation of well-ordered hexagonal mesostructures. Textural properties were found close to those prepared by pure chemicals. SBA-15 after polyethyleneimine impregnation and CMK-3 were tested for carbon dioxide adsorption, successfully demonstrating the possibility of recycling the industrial waste product in a power plant into a useful adsorbent.     

Numerical estimation of hydrogen storage limits in carbon-based nanospaces

Theoretical limits of the hydrogen adsorption in carbon nanospaces are modeled using Monte Carlo simulations. A detailed analysis of storage capacity of slit pores has been performed as a function of the pore size, gas pressure (up to 100 bars) and temperature of adsorption (77 and 298 K). The H₂-slit wall interaction has been modeled assuming energies of adsorption ranging from 4.5 kJ/mol (pure graphene surface) to 15 kJ/mol (hypothetical chemically modified graphene). The quantum nature of H₂ has been incorporated in the calculations using the Feynman-Hibbs approach. It has been shown that in a hypothetical chemically modified porous carbon, with energy of adsorption of 15 kJ/mol or higher and pore size between 0.8 and 1.1 nm, the gravimetric and volumetric storage capacity can achieve targets required for practical applications. The relation between the energy of adsorption and the effective delivery has been discussed.     

Formation of MPEG-PLLA block copolymer microparticles using compressed carbon dioxide

Methoxy poly(ethylene glycol)-b-poly(L-lactide) (MPEG-PLLA) diblock copolymer was synthesized via ring-opening polymerization, and MPEG-PLLA microparticles were then prepared using an aerosol solvent extraction system (ASES) technique with compressed carbon dioxide as antisolvent. The MPEG-PLLA microparticles were prepared at temperatures ranging from 25 °C to 55 °C and at pressures from 85 bar to 150 bar. The concentration of MPEG-PLLA copolymer, solution flow rate, and CO₂ flow rate were adjusted to be 0.5–3.0% (w/v), 0.3–1.0 mL/min, and 19 g/min, respectively. Relatively small spherical microparticles were prepared in the subcritical region at 25 °C, while agglomerated particles were obtained at temperatures above the critical point. The mean particle sizes of the MPEGPLLA microparticles prepared by the ASES varied from 9.53 μm to 46.9 μm depending upon the operating conditions.     

Uses of Ozone in a Three-Phase System for Water Treatment: Ozone Adsorption

A new technique of using ozone for water treatment is presented. This new technique consists of using a three-step-process composed firstly of ozone adsorption on an appropriate adsorbent, secondly water treatment, and thirdly regeneration of the adsorbent. Results regarding ozone adsorption (the first step) are presented in this paper. Different types of silica gel and a type of TiO₂ have been tested for ozone adsorption. It was found that the physical characteristics of the silica gel affect its capacity for ozone. Titanium dioxide has shown ozone decomposition instead of adsorption as it contains Lewis acid sites. An exponential decrease of the silica gel capacity with its moisture content has been found. Linear isotherms in the range of ozone concentrations less than 100?g/m³ NTP have been found. A particle diffusion model with linear equilibrium isotherm has been used to model the breakthrough curves in fixed bed columns.     

An evaluation on PAH degradation and characteristics as media of PVA-derivative hydrogels prepared by using a CGA technique

We manufactured PVA-derived hydrogels wth some crosslinkers by using a foam generation technique. Amino acids gels showed remarkably higher swelling ratios, probably because of the highly crosslinked network along with hydrogen bonds. Boric acid and starch would catalyze dehydration while structuring to result in much lower water content and accordingly high gel content, leading to less elastic, hard gels. Bulky materials such as ascorbic acid or starch produced, in general, large pores, and also nicotinamide, highly hydrophobic, was likely to enlarge its pore size, thus leading to reduced swelling. Hydrophilic (or hydrophobic), functional groups which are involved in the reaction or physical linkage, and bulkiness of crosslinkers were found to be more critical to the crosslinking structure and its density than molecular weights that seemed to be closely related to pore sizes. The average sizes of pores were 20 μm for methionine, 10–15 μm for citric acid, 50–70 μm for L-ascorbic acid, 30–40 μm for nicotinamide, and 70–80 μm for starch. Also, amino acid and glucose gels were more elastic than the others. The elasticity of a gel was reasonably correlated with its water content or swelling ratio. On the other hand, L-ascorbic acid among glucose, methionine, citric acid and vitamins, imparted not only the most favorable physical properties and the greatest cell density but also the highest PAH degradation on its derivative gels. The higher biomass ensured the higher degradation rate. The maximum cell density was 0.267 mg/g-hydrogel and degradation rates and efficiencies ranged 0.013–0.007 mM/mg/day and 92-48%, respectively.