Search results for " Chemical Engineering"
showing 10 items of 2965 documents
Polyacrylates in aqueous solution. The dependence of protonation on molecular weight, ionic medium and ionic strength
2003
Abstract The protonation constants of polyacrylates with different molecular weights ( W =2000–750 000 Da) were determined in different ionic media (alkali metal chlorides and nitrates, tetraalkylammonium chlorides), at 25 °C, by potentiometric measurements (H + –glass electrode). Literature data were also considered. Different models used to analyse protonation data were compared: the first was the modified Henderson–Hasselbalch two-parameter equation, and the second was the three-parameter equation proposed by Hogfeldt. The dependence on the ionic strength of the different supporting electrolytes and all the protonation parameters involved in the two models showed the trend Et 4 N + ≫Li +…
Multiarm star polyglycerol-block-poly(HEMA) as a versatile precursor for the preparation of micellar nanocapsules with different properties
2007
Well-defined multiarm star polymer with hyperbranched polyglycerol as core and poly(2-hydroxyethyl methacrylate) (PHEMA) as arms were used as precursor for the preparation of inverted and aqueous micellar nanocapsules. The partial modification of the hydroxyl groups of PHEMA arms with aliphatic chains led to the formation of inverted micellar nanocapsules. The hydrophilic dye encapsulation capacity of the inverted micelles can be enhanced significantly by transforming the inner hydroxyl groups of PHEMA arms into quaternized amine groups. The modification of the outer and inner hydroxyl groups of PHEMA arms with polyethylene glycol acid chloride and pivaloyl chloride, respectively, resulted …
Sorption characteristics of heavy metal ions by a natural zeolite
2005
Zeolites have been shown to be effective adsorbents for the removal of heavy metals from aqueous solutions. A natural material from Cuba, containing zeolite, has been used for the removal of several metal ions, namely Cu2+, Zn2+, and Ni2+, to evaluate its potential use as a low-cost adsorbent. Batch experiments have been conducted to evaluate the process kinetics and the removal equilibrium at different pH values, metal and zeolite concentrations. Pseudo-second order kinetics and Freundlich equilibrium parameters have been obtained. Results suggested that this natural zeolite has a high potential for heavy metal retention. The selectivity of the studied metals was determined as Cu2+ ≫ Zn2+ …
Evaluation of biosorbents for Cu removal from wastewater in the presence of EDTA
2007
BACKGROUND: This paper evaluates the use of several biosorbents for Cu removal from aqueous solutions in the absence and presence of ethylenediaminetetraacetic acid (EDTA). The objective was to determine the applicability of the sorption process after conventional physicochemical wastewater treatment, or as primary treatment, replacing the physicochemical process. RESULTS: Fixed-bed experiments were performed at Cu influent concentrations of 2 and 20 mg dm−3 and EDTA doses between 0 and 10 mg dm−3. At low Cu concentration without EDTA, Cu uptake capacity followed the order Posidonia oceanica > chitosan > chitin > Scharlau AC > Darco AC, with a maximum, at C/C0 = 0.2, of 23.2 mg g−1. In the …
Synthetic routes to novel fluorogenic pyronins and silicon analogs with far-red spectral properties and enhanced aqueous stability
2020
Fluorogenic detection of reactive (bio)analytes is often achieved with "smart" probes, whose activation mechanism causes the release of aniline-based fluorophores. Indeed, the protection-deprotection of their primary amino is the simplest way to induce dramatic and valuable changes in spectral features of the fluorogenic reporter. In this context, and due to their small size and intrinsic hydrophilicity, we focused on pyronin dyes and related heteroatom analogs (i.e., formal derivatives of 3-imino-3H-xanthen-6-amine and its silicon analog) for their use as optically tunable aniline-based fluorophores. To overcome some severe limitations associated with the use of such fluorogenic scaffolds …
Protein aggregation induced by phase separation in a pea proteins–sodium alginate–water ternary system
2012
Abstract The physicochemical properties of a native, globular plant protein–linear anionic polysaccharide aqueous system at 20 °C were investigated in conditions where biopolymers carry a net negative charge (pH 7.2, 0.1 M NaCl). The pea proteins–sodium alginate mixtures showed a phase separation mainly by thermodynamic incompatibility, characterized at both the macroscopic and microscopic scale. Phase diagram was established and confocal laser scanning microscopy (CLSM) provided accurate data on the microstructure morphology of the system, regarding its phase behavior. In admixture, sodium alginate induced a protein aggregation, certainly by a local depletion of the polysaccharide. Protein…
Removal of drugs in aqueous systens by photoassisted degradation
2005
Aqueous solutions of tetracycline, lincomycin and ranitidine were irradiated with UV light in homogeneous and heterogeneous systems. Two commercial polycrystalline TiO2 powders (Degussa P25 and Merck) were used as photocatalysts. After 5A h, an appreciable photolytic degradation of tetracycline and ranitidine was observed while the degradation of lincomycin was noticeably lower. As far as the mineralization is concerned, a small decrease of the TOC values was measured in the case of tetracycline whereas negligible variations were found for lincomycin or ranitidine. The presence of the photocatalysts greatly enhanced the degradation rates of the drugs with respect to those observed during th…
Study of separation of water + 2-propanol mixture using different ionic liquids: 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide or 1-b…
2018
Abstract The liquid–liquid equilibria data of water (1) + 2-propanol (2) + [bmim][Tf2N] (3) and water (1) + 2-propanol (2) + [bmp][Tf2N] (3) at 283.2, 303.2 and 323.2 K and atmospheric pressure were measured with the objective of understanding the behavior of these two systems and to try to improve the extraction of 2-propanol from water from economical and environmental points of view. The thermodynamic parameters were determined using the non-random two-liquid (NRTL) and universal quasichemical (UNIQUAC) models, and excellent results were achieved in both cases (the maximum root-mean-square deviation was 0.433%). Lastly, the capability of the two ionic liquids to separate 2-propanol from …
Measurement and correlation of liquid-liquid equilibria at different temperatures in water + 1-propanol + 1-ethyl-3-methylimidazolium bis(trifluorome…
2016
Abstract In order to reduce the environmental impact and the economical costs of the separation of 1-propanol from aqueous mixtures, which enables the recycling of the alcohol, the experimental liquid-liquid equilibria (LLE) data of water (1) + 1-propanol (2) + 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf2N]) (3) and water (1) + 1-propanol (2) + 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([hmim][Tf2N]) (3) systems were measured in this work at different temperatures: 283.2, 303.2 and 323.2 K at atmospheric pressure. The results were correlated by non-random two-liquid (NRTL) and universal quasichemical (UNIQUAC) models with good results in both…
Biosorption lead(II) and nikel(II) from an aqueous solution by bacterial biomass
2010
Biosorption lead(II) and nikel(II) from an aqueous solution by bacterial biomass The optimum conditions for biosorption of Pb(II) and Ni(II) from aqueous solution were investigated, by using living and nonliving Pseudomonas fluorescens and Bacillus pumilus isolated from wastewater treatment plant. It was found that the optimum pH for Pb(II) removal by living and nonliving cells was 6.0, while 7.0 for Ni(II) removal. At the optimal conditions, metal ion biosorption was increased as the initial metal concentration increased. The binding capacity by living cells is significantly higher than that of nonliving cells at tested conditions. The maximum biosorption capacities for lead and nickel by …