Articles

February 26, 2014

Abstract

One of the main obstacles impeding implementation of membrane distillation for the recovery and concentration of ammonia from swine manure is wetting caused by fouling.Due to the different types of fouling which can occur in a membrane system, foulants characterization is a complex problem. To elucidate the fouling mechanism, deposit morphology and composition of foulants have been determined using Scanning Electron Microscopy, X-ray Energy Dispersive Spectrometry, Attenuated Total Reflectance Infrared Spectrometry, Ion chromatography and Inductively coupled plasma-optical emission spectroscopy. Based on the analysis of fouled membranes, it is concluded that membrane fouling is dominated by organic fouling in combination with deposits of inorganic elements and microorganisms. After a week of running the membrane process without cleaning, the average fouling layer thickness was estimated to 10e15mm. The fouling layer further results in a loss of membrane hydrophobicity. This indicates that fouling could be a severe problem for membrane distillation performance.

September 09, 2014

Abstract

Excessive livestock production in small areas poses a risk of nitrogen release to the environment and thus air and water contamination. Recovery of ammonia is necessary to avoid overfertilization, but manure management of untreated slurry is costly and complex. The authors discuss ammonium fertilizer recovery from manure using membrane processes and physicochemical methods including technology and energy assessments. Currently, nanofiltration, reverse osmosis, membrane distillation combined with ultrafiltration, and air stripping are the best choices. The processes rely highly on selection of appropriate pretreatment, as residual particulates will lead to fouling of membranes and stripping towers hence affect the performance greatly.

December 21, 2010

Abstract
Complementary theoretical and experimental studies of the consecutive steps of superacid catalyzed polyhydroxyalkylation reactions have been carried out. Calculations for the superacid catalyzed polyhydroxyalkylation of trifluoroacetone and trifluoroacetophenone with aromatic hydrocarbons explained a number of experimental facts within a single theoretical framework of monoprotonation. The principal factors affecting kinetics of superacid mediated hydroxyalkylation were shown to be as follows: (i) the acidity of the

superacid affecting protonation energy of carbonyl components; (ii) the electrophilicity of carbonyl components; and (iii) the nucleophilicity of aromatic components. The modification of those factors allows for tuning of the reactivity of carbonyl and aromatic components; thereby, reaction kinetics are controlled. The conclusions were confirmed by the experiments. Theoretically predicted stoichiometrically imbalanced polymerizations of trifluoroacetone, trifluoroacetophenone, octafluoroacetophenone, and isatin with nonactivated, aromatic hydrocarbons gave high-molecular-weight polymers with a very small excess of the carbonyl compound. The main reasons contributing to the polymerization accelerations were found to be an increase of the first, rate-determining step reaction, and a high efficiency of the superacid catalyzed polyhydroxyalkylations. The present work has thus opened a new route to preparations of polymers of linear, hyperbranched, or hybrid (e.g., linear - hyperbranched) architecture by operating on structural parameters and reaction conditions.

November 29, 2017

Abstract

In our previous work, it was shown that the separation performance of the fixed-site-carrier polyvinylamine (PVAm)composite membrane increases exponentially with increasing relative humidity content in the gas. Through these efforts, it has been important to develop a greater understanding of the relationship between the water, structural, and interfacial properties of the PVAm surface. The degree of hydrophilicity of a given surface plays a crucial role in the separation performance of the membrane when exposed toa humidified gas. Therefore, in the current work, the wettability properties of PVAm at different pHs have been studied by experimental measurements and molecular dynamic simulations. It was confirmed that the intramolecular interactions are not linearly dependent on pH. As well as the H-bonding between protonated and unprotonated amine groups, the conformation polymer chain and the distribution charge density play a crucial role in the surface stability and wettability properties.

January 12, 2017

Abstract

The International Energy Outlook 2010 (IEO2010) reference case reported that world energy‐related carbon dioxide (CO2) emissions would increase from 29.7 billion metric tons in 2007 to 33.8 billion metric tons in 2020 and 42.4 billion metric tons in 2035 [1]. Control of anthropogenic emissions of CO2 is one of the most challenging environmen-tal issues related to global climate change. Carbon capture and sequestration (CCS) could be a promising way to mitigate CO2 emission into atmosphere with the key advantage of continuing to use fossil fuels without causing significant CO2 emissions. The main application of CO2 capture is likely to be at large CO2 point sources: fossil fuel power plants, industrial plants, particularly the manufacture of iron, steel, cement and chemicals, and natural gas plants [2]. Different techniques such as chemical and physi-cal absorption, physical adsorption, cryogenics and membranes can be potentially used for CO2 capture. The technology maturity and development are different, as stated in Figueroa etal. [3]. The innovative CO2 capture technologies (e.g., gas separation mem-branes) suggest that significant cost reduction benefits can potentially be realized once they are commercialized. Membranes as an environmentally friendly technology have already been commercialized in selected gas separation processes such as air separa-tion, natural gas sweetening, biogas upgrading, and hydrogen production during the last two or three decades, and will become steadily more attractive due to their high energy efficiency, relatively low cost, and low environmental impact.

November 14, 2011

Abstract

Multiscale molecular modeling (M3) is applied in many fields of material science, but it is particularly important in the polymer science, due to the wide range of phenomena occurring at different scales which influence the ultimate properties of the materials. In this context, M3 plays a crucial role in the design of new materials whose properties are influenced by the structure at nanoscale. In this work we present the application of a multiscale molecular modeling procedure to characterize polymer/clay nanocomposites obtained with full/partial dispersion of nanofillers in a polymer. This approach relies on a step-by step message-passing technique from atomistic to mesoscale to finite element level; thus, computer simulations at all scales are completely integrated and the calculated results are compared to available experimental evidences. In details, nine polymer nanocomposite systems have been studied by different molecular modeling methods,such as atomistic Molecular Mechanics and Molecular Dynamics, the mesoscale Dissipative Particles Dynamics and the macroscale Finite Element Method. The entire computational procedure has been applied to a number of diverse polymer nanocomposite systems based on montmorillonite as clay and different clay surface modifiers, and their mechanical, thermal and barrier properties have been predicted in agreement with the available experimental data.

October 11, 2012

Abstract

The reactions of acetone, 2,2,2-trifluoroacetone and hexafluoroacetone in methanesulfonic (MSA) and triflicacids (TFSA) with benzene have been studied at M06-2X/6-311+G(d,p) level using cluster-continuum model, where the carbonyl group is explicitly solvated by acid molecules. The introduction of a trifluoromethyl group into the ketone structure reduces the activation energy of the tetrahedral intermediates formation due to an increase of the electrophilicity of the carbonyl group and raises the activation and the reaction energies of the C-O bond cleavage in formed carbinol due to the destabilization of the corresponding carbocation. The introduction of the second trifluoromethyl group inhibits the hydroxyalkylation reaction due to a very strong increase of the reaction and activation energies of the C-O bond cleavage which becomes the rate determining step. The most important catalytic effect of TFSA compared to MSA is not the protonation of the ketone carbonyl, but the reduction of the activation and reaction energies of the carbinol C-O bond cleavage due to better protosolvation properties. Even for TFSA no complete proton transfer to carbonyl oxygen has been ob-served for free ketones. Therefore, the protonation energies of free ketones cannot be considered as a measure of ketone reactivity in the hydroxyalkylation reaction.

May 10, 2012

Abstract

In this work, two computational recipes based on atomistic molecular dynamics simulations are developed and compared to quickly and accurately quantify the interactions of amorphous polypropylene surface with water and oil. Fundamental quantities such as contact angle and surface tension are estimated in excellent agreement with the corresponding experimental values, wheras the comparable values of the work of adhesion obtained using both computational recipes confirm the internal consistency in the presented methodologies.

February 07, 2012

Abstract
Multiscale molecular modelling (MsM) techniques are applied in many fields of material science, but it is particularly important in the polymer field, due to the wide range of phenomena occurring at different scales which influence the ultimate properties of the materials. In this context, MsM plays a crucial role in the design of new materials whose properties are influenced by the structure at the nanoscale. In this work we present the application of a multiscale molecular modelling procedure to characterize a different set of polymer-based nanocomposites (PNCs) obtained with full/partial dispersion of different nanofillers in different polymeric matrices. This approach relies on a step-by step message-passing technique from atomistic to mesoscale to finite element level, and the calculated results are compared to available experimental evidence. In detail, 13 PNC systems have been studied by different molecular modelling methods, such as atomistic molecular mechanics and molecular dynamics, mesoscale dissipative particles dynamics, and macroscale finite element methods, and their mechanical, thermal and barrier properties have been predicted in agreement with the available experimental data.

Abstract

The polyhydroxyalkylation superelectrofílicsyntheses of aldehydes and ketones offer a wide range of of similar but diverse polymer structures otherwise not easily obtainable. By this synthetic method, a set of 7 polymers was prepared and complementary molecular dynamic simulations and experimental studies of the their surface properties of fundamental quantities such as; contact angle, surface tension, work adhesion, interface surface tension of the thin film were estimated in excellent agreement with the corresponding experimental values. 

March 02, 2010

Abstract
Energies of mono- and multiprotonation for 1,2,3-indanetrione and ninhydrin in triflic acid (TFSA) media were estimated at PBE0/aug-cc-pvtz//6-31+G** level of theory. The reactivity of formed intermediates in the reaction of aromatic electrophilic substitution has been studied at the same level of theory. It appears that the basicity of carbonyl groups in 1,2,3-indanetrione is extremely low due to mutual influences of carbonyl groups. Carbonyl 2 is the least basic but the most reactive in accordance with experiment. Calculations demonstrated that monoprotonated intermediates are the principal reactive species in the reaction of hydroxyalkylation of 1,2,3-indanetrione in TFSA. A new isomerization mechanism of 2,2-diaryl-1,3-indanediones to 3-(diarylmethylene) isobenzofuranones in TFSA media has been proposed. Copyright © 2010 John Wiley & Sons, Ltd.

Abstract

The stability and reactivity of mono- and multi-protonatred N-substituted isatin derivatives were studied at PBE0/aug-cc-pvtz//PBE0/6-31þGlevel of theory in triflic acid (TFSA) solution.Calculations showed that the monocationic intermediates are the principal reactive species in the reaction of hydroxyalkylation of isatin derivatives in TFSA media. Electron-withdrawing substituents on the nitrogen atom increase the reactivity of isatin-containing electrophiles towards aromatic hydrocarbons, in accordance with their expected electronic influence. Steric factors also play an important role in the reactivity of isatin-containing electrophiles,especially in the second reaction step, due to their more sterically hindered reactive center.

Abstract

The present research focuses of the complete characterization of interfacial wettability on polymers surface, by the contact angle, binding energies of water and different surfactants on hydrophilic/hydrophobic surface by molecular dynamic simulations. The surfactant used in this work is sodium laurate, CH3(CH2)10COO-Na+while stearic acid (CH3(CH2)16COOH) was employed as the oil model. The polymer surfaces e studied included amorphous polypropylene (a-PP), crystalline polypropylene (PP), polystyrene (PS), and cellulose.  The applied computational methodology yielded a reliable method for interfacial wettability estimation and proved that the developed computational recipe is able to predict the wettability of different surfaces by pure water and different surfactant aqueous solutions in agreement with previous experimental values.

Abstract

The knowledge and control on interfacial wettability of hydrophilic (water) and hydrophobic (oil) substances on octahedral and tetrahedral kaolinite surface is one of the main issues in current practical surface science and interfacial engineering and in the enhance oil recovery as well. Wettability is an important characteristic of solid surfaces and is controlled by the chemical composition and the geometrical structure of the surface. However the degree of affinity of the liquid for a solid surface depends not only on the interaction between the liquid molecules and the surface atoms but also on the interactions between the liquid molecules.These simulations tend to explain the origin of the oil adhesion and water adhesion, regarding of the contact angle measurements, we define that  θ= 0° corresponds to a surface completely wet and θ= > 90°  corresponds partial wet, and θ= < 90° no wet surface.  The kaolinites are moderately hydrophilic (varies from 30 to 36 mJ/m2) and have large negative potentials.