Arrhenius Activation Parameters Research Articles

Generation and study of Am(IV) by temperature-controlled electron pulse radiolysis.

First-of-a-kind temperature-controlled electron pulse radiolysis experiments facilitated the radiation-induced formation of Am(IV) in concentrated (6.0 M) HNO3, and enabled the derivation of Arrhenius and Eyring activation parameters for instigating the radical reaction between NO3˙ and Am(III).

Novel Polyelectrolyte Complex Membranes Containing Carboxymethyl Cellulose–Gelatin for Pervaporation Dehydration of Azeotropic Bioethanol for Biofuel

Polyelectrolyte complex membranes (PECMs) were prepared by combining sodium carboxymethyl cellulose (NaCMC) and gelatin (Ge) with variations in the Ge content in the NaCMC matrix. Characterization methods, such as infrared spectroscopy (FTIR), wide-angle X-ray diffraction (WAXD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), contact angle analysis (CA), and universal testing machines (UTM) were used to investigate the physicochemical studies of the prepared membranes. The pervaporation characteristics of membranes with Ge content were investigated using an azeotropic mixture of water and bioethanol. The obtained data revealed that the membrane with 15 mass% of Ge (M-3) showed a maximum flux of 7.8403 × 10-2 kg/m2·h with separation selectivity of 2917 at 30 °C. In particular, the total and water flux of PECMs are shown as very close to each other indicating that the fabricated membranes could be employed to successfully break the azeotropic point of water-bioethanol mixtures. Using temperature-dependent permeation and diffusion data, the Arrhenius activation parameters were calculated, and the obtained values of water permeation (Epw) were considerably smaller than bioethanol permeation (EpE). Developed membranes showed the positive heat of sorption (ΔHs), suggesting that Henry's sorption mode is predominant.

Gas-Phase Covalent Bond Formation via Nucleophilic Substitution: A Dissociation Kinetics Study of Leaving Groups, Isomeric R Groups, and Nucleophilic Sites.

Nucleophilic substitution covalent modification ion/ion reactions were carried out in a linear quadrupole ion trap between the doubly protonated peptides KGAILKGAILR, RARARAA, and RKRARAA and isomers of either singly deprotonated 3- or 4-sulfobenzoic acid (n-SBA) esterified with either N-hydroxysuccinimide (NHS) or 1-hydroxy-7-aza-benzotriazole (HOBt). The cation/anion attachment product, through which the covalent reaction occurs, was isolated and subjected to dipolar DC (DDC) activation to generate covalently modified product over the ranges of DDC activation energies and times. The resulting survival yields were used to determine reaction rates, and Tolmachev's effective ion temperature was used to extract Arrhenius and Eyring activation parameters. It was found that the kinetics determined under these conditions are highly sensitive to the identities and locations of the nucleophilic sites on the peptides, the leaving groups on the reagent, and the location of the attachment sites on the reagent and analyte. Depending upon the identity of the analyte/reagent combination, significant variations in activation energy or entropy (or both) were both found to underlie the measured rate differences. The determination of dissociation kinetics under DDC conditions and application of Tolmachev's effective ion temperature treatment enables unique insights into the dynamics of gas-phase covalent bond formation via ion/ion reactions.

A comparison of hydrogen release kinetics from 5- and 6-membered 1,2-BN-cycloalkanes

The reaction order and Arrhenius activation parameters for spontaneous hydrogen release from cyclic amine boranes, i.e., BN-cycloalkanes, were determined for 1,2-BN-cyclohexane (1) and 3-methyl-1,2-BN-cyclopentane (2) in tetraglyme. Computational analysis identified a mechanism involving catalytic substrate activation by a ring-opened form of 1 or 2 as being consistent with experimental observations.

Modification of highly brittle polystyrene sulfonic acid‐co‐maleic acid crosslinked sodium alginate membrane into flexible membranes by the incorporation of dibutyl phthalate as a plasticizer for pervaporation separation

AbstractTo convert highly brittle into flexible membrane, the polystyrene sulfonic acid‐co‐maleic acid crosslinked sodium alginate (PSSAMA/NaAlg) membrane was modified by incorporating the different weight% of dibutyl phthalate (DBP) as a plasticizer. The effect of DBP content on the physico‐chemical properties of the membranes was thoroughly examined. The membranes exhibited lower glass transition temperatures with increasing the plasticizer content in the matrix of PSSAMA/NaAlg. The separation performance of the membranes for water/isopropanol and water/1,4‐dioxane was studied at different temperatures. Among the modified membranes, the membrane containing 6 wt% of DBP exhibited the highest separation factors of 24,129 with a flux of 13.57 × 10−2 kg/m2 hr and 23,353 with a flux of 12.99 × 10−2 kg/m2 hr for water/isopropanol and water/1,4‐dioxane at 30°C, respectively. From the temperature‐dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. The estimated activation energy values for permeation of water (Epw) and isopropanol (EpIPA) were, respectively, ranged between 12.09 and 8.79, and 42.52 and 32.79 kJ/mol. A negative heat of sorption (ΔHs) values was obtained for all the membranes, suggesting that Langmuir's mode of sorption was predominant. Based on the results, it is concluded that the modified membranes demonstrated excellent pervaporation performance for the separation of water/isopropanol and water/1,4‐dioxane.

Polyelectrolyte complex membranes made of chitosan—PSSAMA for pervaporation separation of industrially important azeotropic mixtures

Chitosan-based polyelectrolyte complex membranes (PECMs) were developed by incorporating polystyrene sulfonic acid-co-maleic acid (PSSAMA) in the chitosan membrane matrix as a pervaporation membrane by employing a solution technique. Fourier transform infrared (FTIR) spectroscopy, wide-angle X-ray diffraction (WAXD), thermogravimetry analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) were used to characterize the membranes. PECMs were tested for their potentiality to separate various azeotropic mixtures; water/ter-butanol, water/isopropanol, water/n-propanol and water/1, 4 dioxane at their azeotropic point. The PECMs containing 9 mass% of PSSAMA manifest highest separation selectivity of 5352 with a flux of 4.145×10−2 kg /m2h for the azeotropic mixture of water/ter-butanol at 30ᵒC. To confirm their stability at the higher temperature, the PECMs were assessed for pervaporation (PV) separation at 40, 50 and 60ᵒC. For all PECMs total flux and flux of water appeared to be coinciding each other, signifying that PECMs could be used successfully to break the azeotropic point of various azeotropic mixtures. The Arrhenius activation parameters were determined by diffusion and permeation values. The activation energy values procured for water permeation (Epw) were considerably lower than ter-butanol permeation (EpTBOH). The heat of sorption (ΔHs) values obtained for PECMs were negative, showing that Langmuir’s mode of sorption is dominant.

Synthesis and characterization of polyelectrolyte complex membranes for the pervaporation separation of water–isopropanol mixtures using sodium alginate and gelatin

Using a solution technique, polyelectrolyte complex (PEC) membranes were prepared by the complexation of sodium alginate (SA) with gelatin (Ge). The physico-chemical properties of these PEC membranes were studied by Fourier transform infrared spectroscopy (FTIR), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The pervaporation characteristics of membranes were investigated with water–isopropanol mixtures. The effects of Ge content and feed compositions on the pervaporation performance of the membranes were analyzed. The data thus obtained were employed to explain permeation behavior of water and isopropanol through PEC membranes. The experimental results showed that the membrane containing 10 mass% of Ge exhibits the highest separation selectivity of 4277 with a flux of 8.47 × 10−2 kg/m2 h at 30 °C for 10 mass% of water in the feed. The total flux and flux of water are found to be overlapping each other, particularly, for PEC membranes, manifesting that the developed membranes could be used effectively to break the azeotropic point of water–isopropanol mixtures. From the temperature dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. The activation energy values obtained for water permeation (E pw) are significantly lower than those of isopropanol permeation (E pIPA), suggesting that the Ge-incorporated membranes have higher separation ability for water–isopropanol system. The negative heat of sorption (∆H s) values was obtained for all the membranes, suggesting that Langmuir’s mode of sorption is predominant.

Intracrystalline Jump Motion in Poly(ethylene oxide) Lamellae of Variable Thickness: A Comparison of NMR Methods

Helical jumps in poly(ethylene oxide), which are the molecular processes underlying the intracrystalline chain diffusion, are studied on the microseconds to milliseconds time scale by means of NMR. Using a simple proton time-domain technique, a wide range of melt-crystallized morphologies is investigated ranging from extended-chain crystals of short chains to crystals with disordered fold surfaces of longer chains up to 190 kg/mol. From variable-temperature data we directly determine the Arrhenius activation parameters and find that the activation energy is always around 65 kJ/mol. At a given temperature, average correlation times vary from sample to sample over about 1 decade and increase approximately linearly with the lamellar thickness. The observed linear relation is reproduced by a generic Monte Carlo simulation model implementing a mechanism of diffusing defects. The experimental results are compared to 1D carbon-13 MAS exchange NMR (CODEX) and proton rotating-frame relaxation (R1ρ) data, for which...

Development of mesoporous carbon incorporated hybrid membranes for separation of azeotropic mixtures by pervaporation

Using a solution technique, tetraethylorthosilicate crosslinked hybrid poly(vinyl alcohol) membrane was prepared. The membrane was further incorporated with 0, 10, 20, and 30 mass% of mesoporous carbon and the membranes thus obtained were designated as M‐1, M‐2, M‐3, and M‐4, respectively. The physico‐chemical properties of these membranes were investigated using Fourier transform infrared spectroscopy, wide‐angle X‐ray diffraction, differential scanning calorimetry, thermogravimetry analysis, and scanning electron microscopy. The effects of mesoporous carbon and feed composition on pervaporation performance of the membranes were systematically investigated. The membrane M‐4 exhibited the highest separation factor of 4,082 with a flux of 1.93 × 10−2 kg/m2h at 30°C for 10 mass% of water in the feed. Total flux and flux of water are overlapping each other, manifesting that these membranes could be used to break the azeotropic point of water‐isopropanol mixtures effectively. From the temperature dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. The positive heat of sorption values was obtained for M‐1, M‐2, and M‐3, suggesting that Henry's mode of sorption is predominant, giving an endothermic contribution. On the contrary, membrane M‐4 exhibited negative ΔHs value suggesting that the sorption process was dominated by exothermic contribution. POLYM. ENG. SCI., 58:405–415, 2018. © 2017 Society of Plastics Engineers

Dehydration performance of double-network poly(vinyl alcohol) nanocomposite membranes (PVAs-DN)

Double-network poly(vinyl alcohol) nanocomposite membranes (PVAs-DN) were prepared from interpenetrating of two PVA networks. The sequential method was employed in which the first PVA network was completely established from crosslinking of high molecular weight PVA (HPVA) in the presence of silica nanospheres (SNSs) prior to a formation of the second network by the thermal crosslinking of low molecular weight PVA (LPVA). SNSs particle loading was varied at 1 and 3.5wt% which assured an even distribution of the particles in PVAs-DN matrix. Introducing of SNSs enhanced the crystallinity and mechanical properties of PVAs-DN as revealed by XRD and DMA analysis. Furthermore DMA result indicated that HPVA and LPVA networks in PVAs-DN membranes, despite their chemically identical structure, established a separate network and possessed its own relaxation. Effect of temperature on the sorption and the pervaporation was performed using 90wt% ethanol solution. The results showed that the permeability and the selectivity of water were pronouncedly improved in SNSs-filled PVAs-DN membranes compared with unfilled one and HPVA-SN membranes. Consequently thermodynamic parameters and Arrhenius activation parameters were determined.

Restricted Equilibrium Swelling of n‐Alkanes Posed by Ginger Spent Filled Polyurethane Green Composites during Sorption, Desorption, Resorption, and Redesorption Processes

ABSTRACTPolyurethane (PU) based green composites with varying amounts of ginger spent (GS) have been fabricated and characterized for swelling and molecular transport behaviors in n‐alkane probe molecules. Sorption–desorption–resorption–redesorption (S‐D‐RS‐RD) behaviors have been performed to determine the true factor for transport coefficient. Sorption results are obtained by a gravimetric method and diffusion coefficient (D) has been calculated using Fick's equation for the linear data points of time‐dependent sorption/resorption curves. The observation was made that diffusion coefficient follows Fick's rule. Sorption studies have been carried out at 25, 40, and 60°C. A significant increase in sorption values has been noticed with raise in temperature. Sorption (S) and diffusion (D) coefficients of n‐alkanes depend on GS content in PU matrix. From the temperature dependence of diffusion and permeation (P) coefficients, the Arrhenius activation parameters have been used to estimate activation parameters such as diffusion (ED) and permeation (EP). Thermodynamic parameters such as enthalpy (ΔH) and entropy (ΔS) have been interpreted for sorption/resorption results. The percentage weight change for desoption and redesorption processes has been recorded; these results depend on the volatility of the penetrant molecules.

Preparation and pervaporation performance of chitosan-poly(methacrylic acid) polyelectrolyte complex membranes for dehydration of 1,4-dioxane

Polyelectrolyte complex (PEC) membranes composed of chitosan (CS) and poly(methacrylic acid) (PMAA) were prepared by mixing the polymer solutions in different ratios. The chemical interaction and crystallinity of the resulting PEC membranes were respectively analyzed by Fourier transform infrared spectroscopy (FTIR) and wide-angle X-ray diffraction (WAXD). Differential scanning calorimetry (DSC) was used to characterize the thermal properties of the membranes. The membranes thus obtained were subjected to pervaporation (PV) separation of water-dioxane mixtures. Among the PEC membranes, membrane containing 30 wt% ratio of PMAA (M-3) exhibited the highest separation selectivity of 840 with a flux of 12.07 × 10−2 kg/m2h at 30°C at 15 wt% of water in the feed. By the incorporation of NaY zeolite into PEC up to 5 wt%, we have been able to overcome the trade-off phenomenon existing between flux and selectivity in PV process. From the temperature dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. The resulting activation energy values obtained for water permeation (Epw) are much lower than those of dioxane permeation (Epo), suggesting that the developed membranes have higher separation efficiency for water-dioxane system. Based on the heat of sorption (ΔHs) values, the mode of sorption was discussed. POLYM. ENG. SCI., 56:715–724, 2016. © 2016 Society of Plastics Engineers

Development of novel alginate–silica hybrid membranes for pervaporation dehydration of isopropanol

Using a sol–gel technique, organic–inorganic hybrid membranes were prepared by incorporating silica precursors into alginate matrix. Alginate was used as a starting organic polymer, whereas 3-aminopropyl triethoxysilane was used as a counter cation and precursor for the development of inorganic phase. The content of silica gel was controlled by the further addition of tetraethoxysilane (TEOS). The resulting membranes were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetric analysis. After measuring the swelling data at different mass% of water, membranes were subjected for the pervaporation separation of water–isopropanol mixtures in a temperature range of 30–60 °C. The experimental results demonstrated that membrane containing 30 mass% of TEOS showed the highest separation factor of 17,253 with flux of 4.42 × 10−2 kg/m2 h at 30 °C for 5 mass% of water. Except in pure alginate membrane, the values of total flux and flux of water are found to be almost overlapping, suggesting that the developed hybrid membranes could be effectively used to break the azeotropic point of water–isopropanol mixtures. From the temperature-dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. The estimated E p and E D values were ranged between 27.84 and 32.63, and 26.98 and 31.28 kJ/mol, respectively. The positive heat of sorption (∆H s) values was observed in all the membranes, indicating that Henry’s mode of sorption is predominant.

Modification of crosslinked chitosan membrane using NaY zeolite for pervaporation separation of water–isopropanol mixtures

The blocked diisocyanate crosslinked chitosan membrane was modified by incorporating different mass% of NaY zeolite. The physico-chemical properties of resulting composite membranes were studied using Fourier transform infrared spectroscopy (FTIR), wide-angle X-ray diffraction (WAXD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The mechanical properties of the membranes were studied using universal testing machine (UTM). After measuring the equilibrium swelling, membranes were subjected to pervaporation for separation of water–isopropanol mixtures. Both flux and selectivity were increased with increasing NaY zeolite content in the membranes. The membrane containing 40 mass% of NaY zeolite exhibited the highest separation selectivity of 11,241 with a flux of 11.37×10−2kg/m2h for 10 mass% of water in the feed. The total flux and flux of water are almost overlapping each other, suggesting that these membranes could be effectively used to break the azeotropic point of water–isopropanol mixture. From the temperature dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. All the composite membranes exhibited lower activation energy compared to crosslinked membrane, indicating that the permeants require less energy during the process because of molecular sieving action attributed to the presence of sodalite and super cages in the framework of NaY zeolite. The Henry's mode of sorption dominates the process, giving an endothermic contribution.

Synthesis and characterization of GTMAC grafted chitosan membranes for the dehydration of low water content isopropanol by pervaporation

Glycidyltrimethylammonium chloride (GTMAC) grafted chitosan (CS) membranes were prepared by the solution casting technique. The chemical composition and morphological characteristics of the prepared GTMAC/CS membranes were investigated by various techniques such as Fourier transform infrared (FTIR) spectroscopy, wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The effects of grafting and feed composition on pervaporation performance of the membranes were systematically studied. The membrane containing 40 mass% of GTMAC exhibited the highest separation selectivity of 2133 with a flux of 6.91×10−2kg/m2h at 30°C for 10 mass% of water in the feed. The total flux and flux of water are almost overlapping each other, manifesting that these membranes could be used effectively to break the azeotropic point of water–isopropanol mixture. From the temperature dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. The activation energy values obtained for water permeation (Epw) are significantly lower than those of isopropanol permeation (EpIPA), suggesting that the grafted membranes developed here have higher separation ability for water-isopropanol system. The positive heat of sorption (ΔHs) values was obtained for all the grafted membranes, suggesting that the Henry's mode of sorption is predominant.

Pervaporation separation of water–isopropanol mixtures using silicotungstic acid loaded sulfonatedpoly(ether ether ketone) composite membranes

Composite membranes of sulfonatedpoly(ether ether ketone) (sPEEK) containing nascent and modified silicotungstic acid (STA) nanoparticles were tested for pervaporation (PV) separation of water–isopropanol mixtures. The performance of filler loaded composite membranes was better than that of nascent polymer membranes. The chemically modified STA containing membranes showed improved PV performance compared to those of nascent STA loaded membranes. This effect is attributed to leaching of STA during the PV cycles. The leaching effect was reduced after modification of STA with cesium carbonate. Among all the composite membranes prepared by the solution casting method, the membrane containing 7 wt% modified STA gave the highest PV separation performance compared to those containing 3, 5 and 10 wt% STA. The PV performance of the 7 wt% STA loaded membrane was further tested as a function of feed water composition from 10 to 25 wt% and a temperature range of 30–60 °C. Characterization of the membranes was done by universal testing machine (UTM), scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques. The PV results have been explained in terms of sorption–diffusion principles and Arrhenius activation parameters.

Characterizing intermediates along the transition from polyproline I to polyproline II using ion mobility spectrometry-mass spectrometry.

Polyproline exists predominately as the all-cis polyproline I (PPI) helix in aliphatic alcohols, whereas the all-trans polyproline II (PPII) helix is favored in aqueous solutions. Previous ion mobility spectrometry-mass spectrometry (IMS-MS) work demonstrates that the gas-phase conformations of polyproline ions can be related to the corresponding PPI and PPII helices in solution [J. Phys. Chem. B 2004, 108, 4885]. Here, we use IMS-MS to examine the detailed intermediate steps associated with the process of Polyproline-13 (Pro13) conversion from the PPI helix to the PPII helix upon solvent exchange. Collision cross section distributions of Pro13 [M + 2H](2+) ions obtained at different transition times indicate the presence of two major conformers, identified as the PPI and PPII helices, and six conformers that appear as subpopulations of polyproline. Further analysis shows a transition mechanism with sequential cis-trans isomerizations followed by a parallel process to establish PPII and two smaller subpopulations at equilibrium. Temperature-dependent studies are used to obtain Arrhenius activation parameters for each step of the mechanism, and molecular dynamics simulations provide insight about the structures of the intermediates. It appears that prolines sequentially flip from cis to trans starting from the N-terminus. However, after the first few transitions, possible steps take place at the center of the peptide chain; subsequently, several pathways appear to be accessible at the same time. Our results reflect the existence of stable subpopulations in polyprolines and provide new insight into the structural changes during the transition process of polyproline peptides converting from PPI to PPII in aqueous solution.

Barrier properties of celluloses microfibers (CMF)/ethylene-co-vinyl acetate (EVA)/composites

The effect of celluloses microfibers (CMF) reinforcement in ethylene-vinyl acetate (EVA) on its barrier properties was evaluated using xylene, toluene, and benzene as penetrant molecule. CMF were obtained from Hibiscus sabdariffa by steam explosion technique and was reinforced in EVA by melt extrusion. The barrier properties of the composites were found to be improved with CMF loading. This has been attributed to good interfacial interaction between CMF and EVA which is further confirmed using Kraus equation. Arrhenius activation parameters for the diffusion, permeation, and thermodynamic parameters were also estimated from the sorption data. The mode of the transport was found to follow regular Fickian trend.

Solvent transport phenomenon of cellulose microfiber (CMF) reinforced poly (ethylene-co-vinyl acetate) (EVA) composites

Composite films based on EVA with CMF were prepared and characterized for their solvent transport nature. CMF were derived from Hibiscus sabdariffa by steam explosion technique and incorporated in the EVA matrix by extrusion. Solvent transport by the composites was analyzed using hexane, heptane and octane as penetrant molecules. The solvent uptake behavior of EVA/CMF composites is explained on the basis of the penetrant size, temperature and the filler loading. The composite had improved barrier property compared with unfilled EVA. This in turn is an indication of good fiber-matrix interaction in the composite system. Diffusion parameters such as diffusion coefficient, permeation coefficient and Arrhenius activation parameters and thermodynamic parameters such as enthalpy and entropy were evaluated in detail. The mode of transport was found to be Fickian.

Kinetics of Oxidation of Amino Acids by a Newly Synthesized Oxidant, N-Chloropyrazinamide in Aqueous Acetic Acid Medium

The kinetics of oxidation of amino acids namely, alanine, glycine, leucine, phenyl alanine and valine by N-chloropyrazinamide (NCPZA) in aqueous acetic acid medium in the presence of hydrochloric acid have been investigated. The observed rate of oxidation is first order in [NCPZA], [H+] and [Clˉ]. The order with respect to [amino acid] is zero. The rate of oxidation increases with increase in the percentage of acetic acid. The reaction rate increases slightly with increase in ionic strength, while retards with addition of pyrazinamide. Arrhenius and thermodynamic activation parameters have been evaluated from Arrhenius plot by studying the reaction at different temperatures. A most probable reaction mechanism has been proposed and an appropriate rate law is deduced toaccount for the observed kinetic data.