Sub-ambient Temperatures Research Articles

Sub-ambient air separation via Li+ exchanged zeolite

In this study, we extend the concept of adsorptive air separation using zeolites to sub-ambient temperature conditions. Sub-ambient temperature conditions investigated in this study (210–270 K) enable larger swing capacities for solid adsorbents under significantly milder conditions than those required by cryogenic distillation systems. Experimental O2 and N2 isotherms—measured in a wide range of temperatures (150 K–300 K)—were utilized to construct multicomponent isotherms (IAST) and estimate the temperature-dependent separation performances of Li+-exchanged type X zeolite (Si/Al ratio ∼1) under synthetic air mixture (22 mol% O2 and 78 mol% of N2). As temperature decreases from ambient conditions, the IAST selectivity (N2/O2) increases. Sorption breakthrough tests at 240 K with synthetic air mixtures further validated the enhanced swing capacity and selectivity provided by sub-ambient conditions. Dual-bed vacuum pressure swing adsorption (VPSA) experiments at sub-ambient temperatures were compared to standard VPSA experiments at room temperature. The sub-ambient temperature (240 K) application of VPSA process using synthetic air mixture produced O2 with a purity over 99% and recovery over 56%, surpassing the VPSA performance at ambient temperature conditions (298 K). The separation process investigated in this study could potentially be coupled to certain cryogenic air separation units to reduce the overall energy cost of the unit by supplying O2 enriched stream into the distillation system.

Understanding intrinsic plasticizer in vegetable oil-based polyurethane elastomer as enhanced biomaterial

Renewable polyol is of increasing interest as a building block in biomedical elastomer for bearing biodegradable ester group and immaculate functionality. Derived from non-edible vegetable oil, a new class of elastomer was successfully functionalized with MDI and TDI. Crosslink densities were varied by regulating ratio of hydroxyl to diisocyanate (r) at 1/1.0, 1/1.1, and 1/1.2. Produced elastomers were examined by crosslink density, attenuated total reflectance Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis, tensile testing, and scanning electron microscopy. The obtained elastomers had subambient glass transition temperature (T g) suggested majority soft segment that acted as a continuous phase with intermediate phase separation. Medium conversion at gel point had enhanced physical properties. Highly elastic mechanical behavior was afforded from combination of side chains and high molecular weight polyol. At r = 1/1.2, MDI-based elastomer showed twofold improvement in Young modulus at slight expense of elongation. TDI-based elastomer accomplished elongation beyond 162%. Branching allophanate and biuret resisted early thermal breakdown by elevating activation energy. Frequency response and kinetic of thermal degradation provided beneficial perspective for elastomer characterization. The vegetable oil-based polyurethane was found able to resemble most of the physical properties of polycaprolactone (PCL)-derived polyurethane.

Spectroscopic Studies of How Moisture Enhances CO Oxidation over Au/BN at Ambient Temperature

Gold catalysts readily catalyze CO oxidation at subambient temperature, wherein moisture can influence the activity, typically with a volcano-shaped dependence. In this study, we examine moisture-enhanced CO oxidation over Au/BN. The room-temperature CO oxidation activity of Au/BN increases quickly with increasing moisture content up to 100% relative humidity (RH). In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and in situ UV–vis diffuse reflectance spectroscopy (UV-vis-DRS) demonstrate that mainly metallic gold is present on the h-BN support. Surface intermediates are found when moisture is fed together with CO and O2, attributable to *CO(H2O)n and *OOH, respectively. These surface intermediates are reactive when counter-reactant is purged. Injection of isotope-labeled H218O demonstrates that OH from H2O takes part in the process of CO2 formation. The results of this study provide direct evidence showing moisture-enhanced CO adsorption, moisture-enhanced O2 adsorption, and t...

Unexpected differences between planar and column liquid chromatographic retention of 1-acenaphthenol enantiomers controlled by supramolecular interactions involving \u03b2-cyclodextrin at subambient temperatures

We report the results of experimental work focusing on host-guest supramolecular complex creation between macrocyclic compound (β-cyclodextrin) and 1-acenaphthenol enantiomers (racemic mixture) in liquid phase composed of 35% acetonitrile in water (v/v) at different temperatures ranging from 0 to 90 °C. Experimental setup involved several analytical protocols based on classical non-forced flow planar chromatography (RP-18 TLC plates), micro-TLC (RP-18 W HPTLC plates), column chromatography (HPLC with C-18 and C-30 stationary phases), as well as UV-Vis spectrophotometry and optical microscopy. It has been found that under various planar chromatographic conditions (stationary plates type, chamber shape and volume, development mode, and saturation) non-typical retention properties (extremely high retention) of 1-acenaphthenol at subambient temperatures can be observed. To our knowledge, reported experimental results are in opposition to currently described retention models based on column chromatographic investigation of host-guest complexes (where in case of strong interaction of given analyte with macrocyclic mobile phases additive, which itself is non strongly retarded by stationary phase—close to the retention of dead volume marker, the retention of target compounds is shortened at low temperatures). To explain this TLC phenomenon that may have in our opinion a number of practical applications, especially for selective high throughput separation involving microchromatographic and/or microfluidic devices as well fractionation and extraction protocols (using, e.g., bar extraction systems), several experiments were conducted focusing on (i) acenaphthenol chromatography under different instrumental conditions, (ii) cyclodextrin retention measured as analyte or mobile phase additive, (iii) plate development time under different mobile phases and temperature settings, (iv) various column chromatographic conditions including C-30 and two C-18 stationary phases, (v) UV-Vis spectrophotometry, and (vi) microscopy inspection of precipitated CD-acenaphthenol crystals. Analysis of collected data has revealed that the most probable reasons for TLC retention behavior of 1-acenaphthenol under β-cyclodextrin additive conditions can be associated with (i) solubility changes of created host-guest complex, (ii) kinetics of solid complex precipitation, and (iii) differences in analysis time between planar and column chromatography. Because precipitation phenomenon may have a massive impact on analytes quantification involving macrocycles as the mobile phase additives, our previously reported data concerning a number of low-molecular compounds (mainly steroids and non steroidal endocrine disrupting chemicals) using HPLC methodology based on binary mobile phases without and with β-cyclodextrin and its hydroxypropyl derivative were re-examined and results discussed. Considering these data and the whole data set reported presently, the enhanced model of chromatographic retention driven by host-guest interaction was proposed.

Deformation and Failure of Ultrafine-Grained Cu at Subambient Temperature

The ultrafine-grained copper was obtained by 12 passes of equal-channel angular pressing method. The uniaxial tensile tests at room temperature and the subambient temperature of 77 K show that the yield stress increases from the value of 128 MPa to the value of 138 MPa, respectively. In addition, the lowering the test temperature tends to the increase of the deformation before the failure. The fractographic analysis shows the transcrystalline ductile failure for all samples. Due to the high plasticity of nanostructured copper no influence of the nanoporosity on the failure process was observed.

Development of Two-Step Temperature Process to Modulate the Physicochemical Properties of β-lactoglobulin Nanoparticles.

The development of a new manufacturing process, a two-step temperature treatment, to modulate the physicochemical properties of nanoparticles including the size is critical. This is because its physicochemical properties can be key factors affecting the cellular uptake and the bioavailability of bioactive compounds encapsulated in nanoparticles. The aims of this study were to produce (beta-lactoglobulin) β-lg nanoparticles and to understand how two-step temperature treatment could affect the formation and physicochemical properties of β-lg nanoparticles. The morphological and physicochemical properties of β-lg nanoparticles were determined using atomic force microscopy and a particle size analyzer, respectively. Circular dichroism spectroscopy was used to investigate the secondary structure of β-lg. The surface hydrophobicity and free thiol groups of β-lg were increased with a decrease in sub-ambient temperature and an increase in mild heat temperature. As sub-ambient temperature was decreased, a decrease in α-helical content and an increase in β-sheet content were observed. The two-step temperature treatment firstly involved a sub-ambient temperature treatment from 5 to 20°C for 30 min, followed secondly by a mild heat temperature treatment from 55 to 75°C for 10 min. This resulted in the production of spherically-shaped particles with a size ranging from 61 to 214 nm. Two-way ANOVA exhibited the finding that both sub-ambient and mild heat temperature significantly (p<0.0001) affected the size of nanoparticles. Zeta-potential values of β-lg nanoparticles were reduced with increasing mild heat temperature. In conclusion, two-step temperature treatment was shown to play an important role in the manufacturing process – both due to its inducement of the conformational changes of β-lg during nanoparticle formation, and due to its modulation of the physicochemical properties of β-lg nanoparticles.

Investigating foamed polylactic acid films through cell structure alteration and processing conditions

Polylactic acid films were foamed through a solid-state process using liquid carbon dioxide as a physical blowing agent. The foamed films were stretched to understand the effect of cell strut alignment on elastic modulus and yield stress normalised with density. Through stretching, cell strut alignment was achieved and verified with scanning electron microscopy. Aligning the cell struts improved the elastic modulus by a factor of 4 and the yield stress by a factor of 5 while decreasing the strain percentage at break. Aligned cell struts axially strain during tensile deformation which requires more force than unaligned cell struts which bend at initial deformations. The flexographic printability and surface topography of the foamed polylactic acid films was also analysed. The temperature used to impregnate carbon dioxide into the polylactic acid films was varied to understand its significance on printability and surface topography. Samples impregnated at ambient temperatures had smooth surface topography and a shiny lustre and good printability, whereas, samples impregnated at sub-ambient temperatures had a dull and rough texture and poor printability. Also, the carbon dioxide content had an effect on the surface topography and printability.

Structure of Mixtures of Water and Methanol Derived from Their Cohesive Energy Densities and Internal Pressures from Subambient Temperatures to 473 K.

The cohesive energy densities, ced, and the internal pressures, Pint, of aqueous methanol mixtures are calculated from literature data for the entire composition range over a temperature range of 273-473 K, at saturation pressures up to 373 K and at 7.0 MPa above this temperature. Ratios Pint/ced are measures of the "structuredness" of the studied fluids, and the small values noted signify "tight" structures, due to hydrogen bonding. The "tighter" the structure, the larger is the surface tension of the mixtures (at 298.15 and 323.15 K). This structural feature diminishes in intensity as the temperature and the methanol contents are increased, except in cold (≤298 K) and hot (≥423 K) water-rich mixtures. Under such exceptional conditions, the hydrogen-bonded structure of water is enhanced.

Optimal process design for recovering effluent gas at subambient temperature

Effluent gas is common in the petrochemical industry. The recovery of effluent gas is of great importance to resource recycle and environmental protection. However, low concentration, low boiling point feature of petrochemical effluent decreases the recovery economy. This article presents a systematic approach to design process networks for recovering effluent gas at subambient temperature. An effluent recovery superstructure that contains HENS (Heat Exchanger Network Synthesis) operator, pressure operator and separation operator is proposed. In addition, multicomponent nonisothermal phase change of streams are allowed inside the HENS operator. Since the process streams exhibit nonlinear temperature-enthalpy relations (T-H curve), we correlate the enthalpy (H) with temperature (T), pressure (P) and compositions (m) of the process streams by a cubic polynomial function to balance the nonlinearity and accuracy of the state equations. The objective of the model is to maximize total annualized revenue by regulating connecting structures as well as operating parameters. Two industry cases are presented to show the accuracy and effectiveness of the proposed approach.

Catalytic routes to fuels from C1 and oxygenate molecules.

This account illustrates concepts in chemical kinetics underpinned by the formalism of transition state theory using catalytic processes that enable the synthesis of molecules suitable as fuels from C1 and oxygenate reactants. Such feedstocks provide an essential bridge towards a carbon-free energy future, but their volatility and low energy density require the formation of new C-C bonds and the removal of oxygen. These transformations are described here through recent advances in our understanding of the mechanisms and site requirements in catalysis by surfaces, with emphasis on enabling concepts that tackle ubiquitous reactivity and selectivity challenges. The hurdles in forming the first C-C bond from C1 molecules are illustrated by the oxidative coupling of methane, in which surface O-atoms form OH radicals from O2 and H2O molecules. These gaseous OH species act as strong H-abstractors and activate C-H bonds with earlier transition states than oxide surfaces, thus rendering activation rates less sensitive to the weaker C-H bonds in larger alkane products than in CH4 reactants. Anhydrous carbonylation of dimethyl ether forms a single C-C bond on protons residing within inorganic voids that preferentially stabilize the kinetically-relevant transition state through van der Waals interactions that compensate for the weak CO nucleophile. Similar solvation effects, but by intrapore liquids instead of inorganic hosts, also become evident as alkenes condense within MCM-41 channels containing isolated Ni2+ active sites during dimerization reactions. Intrapore liquids preferentially stabilize transition states for C-C bond formation and product desorption, leading to unprecedented reactivity and site stability at sub-ambient temperatures and to 1-alkene dimer selectivities previously achieved only on organometallic systems with co-catalysts or activators. C1 homologation selectively forms C4 and C7 chains with a specific backbone (isobutane, triptane) on solid acids, because of methylative growth and hydride transfer rates that reflect the stability of their carbenium ion transition states and are unperturbed by side reactions at low temperatures. Aldol condensation of carbonyl compounds and ketonization of carboxylic acids form new C-C bonds concurrently with O-removal. These reactions involve analogous elementary steps and occur on acid-base site pairs on TiO2 and ZrO2 catalysts. Condensations are limited by α-H abstraction to form enolates via concerted interactions with predominantly unoccupied acid-base pairs. Ketonization is mediated instead by C-C bond formation between hydroxy-enolates and monodentate carboxylates on site pairs nearly saturated by carboxylates. Both reactions are rendered practical through bifunctional strategies, in which H2 and a Cu catalyst function scavenge unreactive intermediates, prevent sequential reactions and concomitant deactivation, and remove thermodynamic bottlenecks. Alkanal-alkene Prins condensations on solid acids occur concurrently with alkene dimerization and form molecules with new C-C bonds as skeletal isomers unattainable by other routes. Their respective transition states are of similar size, leading to selectivities that cannot sense the presence of a confining host. Prins condensation reactions benefit from weaker acid sites because their transition states are less charged than those for oligomerization and consequently less sensitive to conjugate anions that become less stable as acids weaken.

An acyclic zincagermylene: rapid activation of dihydrogen at sub-ambient temperature.

The first example of a stable zincagermylene, :Ge(TBoN)(ZnL*) (TBoN = N(SiMe3){B(DipNCH)2}, Dip = C6H3Pri2-2,6; L* = -N{C6H2[C(H)Ph2]2Me-2,6,4}(SiPri3)) is prepared and shown to have unprecedented reactivity for a germylene, with respect to the activation of dihydrogen. Computational analyses point towards this being partially derived from the electron releasing nature of the amido-zinc fragment, which leads to a narrowing of the HOMO-LUMO gap in the compound.

Characterization of Polyurethane Coated Aerospace Aluminium Alloy (7075) By DSC, XRD and Adhesion Test

The research is envisaging characterizing the Polyurethane (PU) coating on AA 7075 so as to predict the aircraft coating life. Differential Scanning Calorimetry (DSC) and X-ray Diffractometry have been employed to investigate the differences in thermal behavior and crystalline structure of the polyurethane (GB BOND 141). DSC can be used to examine the material from a subambient starting temperature to the glass transition event and finally through the crystalline melting region. X-ray diffraction (XRD) provides important structural information about the polyurethane in the structure of semi-crystalline polymer substance consisting of two phases, viz., amorphous and crystalline as well as their fine texture which has a strong effect on physical and mechanical properties of polyurethane. After analyzing the characteristics, the extent of coating loss is examining visually in order to evaluate the adhesion property before carrying out the peel-off test.

An apparatus to measure the thermal conductivity of insulation panels at sub-ambient temperature

A single-sided guarded-plate apparatus has been developed to measure the thermal conductivity of insulation panels of sub-meter size at sub-ambient temperatures ranging from 250 to 300 K. This apparatus allows thermal conductivity measurements to be performed at large temperature differences simulating the actual operating conditions in an application and can accommodate panels of various thickness. The cold plate in the apparatus is cooled with a flow thermostat. The reduction in performance due to the heat conductance along the edge of a vacuum insulation panel is significant at small panel sizes and is detrimental to the end application. The effective thermal conductivity of square vacuum insulation panels of several thickness and area is measured, and is observed that the square panels of side 10 and 20 cm have about twice higher thermal conductivity than their larger counterparts due to the heat leak along the edges of these panels.

Effect of Urea Concentration on the Viscosity and Thermal Stability of Aqueous NaOH/Urea Cellulose Solutions

Aqueous solutions of sodium hydroxide (NaOH) and urea are a known and versatile solvent for cellulose. The dissolution of cellulose occurs at subambient temperatures through the formation of a cellulose-NaOH-urea “inclusion complex” (IC). NaOH and urea form a hydrate layer around the cellulose chains preventing chain agglomeration. Urea is known to stabilize the solution but its direct role is unknown. Using viscometry and quartz crystal microbalance with dissipation monitoring (QCM-D) it could be shown that the addition of urea reduced the solutions viscosity of the tested solutions by almost 40% and also increased the gelation temperature from approximately 40°C to 90°C. Both effects could also be observed in the presence of additional cellulose powder serving as a physical cross-linker. Using Fourier transform infrared (FTIR) spectroscopy during heating, it could be shown that a direct interaction occurs between urea and the cellulose molecules, reducing their ability to form hydrogen bonds with neighbouring chains.

Influence of cross-linking agents and curing condition on the performance of epoxy coating

Purpose The performance of epoxy coating on metal substrate at low temperature and high humidity application has adverse effect on cure rate, film properties and adhesion. In recent years, several advanced amine cross-linking agents having superior curing ability at low temperature application environment have been introduced. The aim of this paper is to study the properties of epoxy-based coating cured with different cross-linking agents designed for low temperature application at different environmental conditions. Design/methodology/approach Series of cross linking agents such as modified cycloaliphatic amine (H1), polyamine adduct (H2), modified aliphatic ketamine (H3), phenalkamine (H4) and phenalkamide (H5) have been studied to evaluate their performance in epoxy compositions when cured at four environmental conditions, i.e. at ambient and sub-ambient temperatures with 60 and 90 per cent relative humidity, respectively. The effect of curing conditions was investigated by evaluating different physico-mechanical properties. Dynamic mechanical analyser technique was used to determine glass transition temperature (Tg) and cross-link density (ρ) of coatings. Anticorrosive properties of coatings also have been studied by electrochemical impedance spectroscopy. Findings The outcome of this study is expected to generate new insight into the curing behaviour of epoxy coating using different cross-linking agents which are recommended for low temperature application. Optimum physico-mechanical and corrosion resistance properties have been obtained by phenalkamine curing agent at low temperature and high humidity condition. Practical implications This study is an experimental approach to select the better cross-linking agent for low temperature application. Different test conditions were measured for understanding the performance of epoxy coating cured at different environmental condition. Originality/value The understanding reaction mechanism of the epoxy resin with cross-linking agent at different environmental condition is the great challenge and is hardly investigated in the literature. Therefore, in this research, the influence of climatic conditions and type of cross-linking agents on curing behaviour of epoxy-based coating was investigated.

Time and Voltage Resolved Investigation of Lithium Plating on Graphite Anodes By Operando Electron Paramagnetic Resonance (EPR) Spectroscopy

Graphite is the standard anode material in Li-ion cells due to its high capacity of 372 mAh g-1, good cycling stability and low price. Lithium ions can reversibly intercalate into the graphite host structure at low potentials of 80 – 120 mV vs. Li/Li+. While the low intercalation potential is favorable in terms of energy density, it can cause lithium plating if cells are charged at high rates or at low temperatures. Lithium metal plating adversely affects the cell life due to the loss of active lithium and electrolyte and also poses a serious safety hazard because of internal short circuiting of the cell. For the development of fast and safe charging protocols, a detailed understanding of the plating mechanism is necessary, as lithium plating is the rate limiting step during the charge of Li-ion cells. Unfortunately, there are no analytical techniques available to directly monitor the occurrence of lithium plating on graphite anodes during cell operation, expect for a recent operando neutron diffraction analysis.[1] In general, lithium plating is only indirectly observed based on specific features in the subsequent discharging profile[2] or on the observation of decreasing Coulombic efficiencies[3]. Both methods are elegant and simple, but also have specific limitations: the former fails to detect electrochemically inactive “dead” lithium, while the latter cannot distinguish whether the missing lithium is present in the metallic state (dead lithium) or in ionic form (SEI components). Additionally, microscopic techniques can yield valuable structural and morphological information regarding lithium metal deposits, but are limited to post-mortem analysis of cycled electrodes. In a previous publication,[4] we showed that operando electron paramagnetic resonance (EPR) spectroscopy can be used for the detection of mossy lithium formation on lithium metal anodes. In the present work we extend this concept and suggest to also use operando EPR spectroscopy for the time/voltage resolved and semi-quantitative detection of lithium metal plating on graphite anodes upon cell charge. The spectro-electrochemical cell design has been adapted to implement a reference electrode for the precise determination of the graphite electrode potential. Firstly, the good homogeneity of the electrochemical processes in the EPR cell design are demonstrated, exploiting the characteristic color change of the graphite electrode as a function of the state of charge. In the next step, lithium plating is forced on a fully lithiated graphite electrode. The upper panel in Figure 1 shows the typical voltage profile for a galvanostatically controlled lithium plating process. The exemplary EPR spectra (Figure 1b), measured at positions as indicated in Figure 1a, show two distinct features which differ in signal width and can therefore be discriminated. The broader signal can be assigned to lithium intercalated in graphit (LiCx) and the very narrow signal to metallic lithium. The nearly linear increase of the lithium metal signal intensity (lower panel in Figure 1a) nicely displays the semi-quantitative nature of the EPR technique. Then, the influence of the charging rate on both the amount and the reversibility of lithium metal plating is investigated. It is found, that the amount of plated lithium increases with the charging rate whereas the reversibility decreases. According to a comparison of the EPR results with the Coulombic inefficiency, the majority of the “missing” lithium is “dead” lithium, i.e., it remains trapped in the graphite anode in its metallic form without electrical contact to the electrode. Lastly, the lithium plating process is also investigated at sub-ambient temperatures and in the presence of electrolyte additives. The results are discussed in the context of designing a fast and safe charging protocol.

Terpene Based Sustainable Elastomer for Low Rolling Resistance and Improved Wet Grip Application: Synthesis, Characterization and Properties of Poly(styrene-co-myrcene)

Incited by the unprecedented surge of developing sustainable polymers, we demonstrate herein a green emulsion polymerization route toward the development of sustainable rubbery materials based on β-myrcene (MY) and styrene (ST) for low rolling resistance and improved wet grip applications. The microstructure of the synthesized copolymers was found to be governed by the ST weight percent. For example, the copolymers having less than 40 wt % of ST had 1,2 vinyl and 3,4 addition products along with 1,4-cis and -trans microstructure of the polymyrcene unit, whereas the copolymers having higher weight percent of ST had only 1,4-cis and -trans microstructure of the polymyrcene unit. The copolymers displayed improved onset degradation temperature and subambient glass transition temperatures. The copolymer having a 70/30 weight/weight ratio of MY/ST displayed a molecular weight of 51 500 Da and a glass transition temperature of −35.2 °C. The 70/30 rubber vulcanizate exhibited satisfactory mechanical properties (t...

Improving the Sensitivity, Resolution, and Peak Capacity of Gradient Elution in Capillary Liquid Chromatography with Large-Volume Injections by Using Temperature-Assisted On-Column Solute Focusing.

Capillary HPLC (cLC) with gradient elution is the separation method of choice for the fields of proteomics and metabolomics. This is due to the complementary nature of cLC flow rates and electrospray or nanospray ionization mass spectrometry (ESI-MS). The small column diameters result in good mass sensitivity. Good concentration sensitivity is also possible by injection of relatively large volumes of solution and relying on solvent-based solute focusing. However, if the injection volume is too large or solutes are poorly retained during injection, volume overload occurs which leads to altered peak shapes, decreased sensitivity, and lower peak capacity. Solutes that elute early even with the use of a solvent gradient are especially vulnerable to this problem. In this paper, we describe a simple, automated instrumental method, temperature-assisted on-column solute focusing (TASF), that is capable of focusing large volume injections of small molecules and peptides under gradient conditions. By injecting a large sample volume while cooling a short segment of the column inlet at subambient temperatures, solutes are concentrated into narrow bands at the head of the column. Rapidly raising the temperature of this segment of the column leads to separations with less peak broadening in comparison to solvent focusing alone. For large volume injections of both mixtures of small molecules and a bovine serum albumin tryptic digest, TASF improved the peak shape and resolution in chromatograms. TASF showed the most dramatic improvements with shallow gradients, which is particularly useful for biological applications. Results demonstrate the ability of TASF with gradient elution to improve the sensitivity, resolution, and peak capacity of volume overloaded samples beyond gradient compression alone. Additionally, we have developed and validated a double extrapolation method for predicting retention factors at extremes of temperature and mobile phase composition. Using this method, the effects of TASF can be predicted, allowing determination of the usefulness of this technique for a particular application.

Post-combustion carbon dioxide capture via 6FDA/BPDA-DAM hollow fiber membranes at sub-ambient temperatures

Abstract Post-combustion carbon dioxide capture has the greatest near-term potential compared to other technological pathways to mitigate CO2 emissions. The hybrid membrane and cryogenic distillation process developed at American AirLiquide allows sub-ambient temperature (−50 °C to −20 °C) CO2 capture to be cost effective. In previous work, Matrimid® hollow fiber membranes with so-called “nodular” selective layers were successfully formed and showed a combination of high selectivity and high permeance at temperatures below −20 °C. Despite good performance, considering the low CO2 concentration and large volume of flue gas to be treated, the permeance of the “nodular” Matrimid® fibers still required improvement. In this work, a new membrane material with higher fractional free volume than Matrimid®, 6FDA/BPDA-DAM (1:1), was investigated for sub-ambient temperature (SAT) CO2 capture. Defect free 6FDA/BPDA-DAM hollow fiber membranes were successfully formed; however, the bare fibers lost selectivity at temperatures below 0 °C, possibly due to the development of minor defects in the thin selective layer. This problem was corrected by post-treatment with polydimethyl siloxane (PDMS). The PDMS post-treated 6FDA/BPDA-DAM hollow fiber membranes displayed much higher permeance than the Matrimid® fibers with a high selectivity. The high selectivity is presumably due to additional polymer backbone rigidity at SAT conditions combined with possible local chain orientation; and the high permeance is believed to be a result of hindered packing of the polymer backbone.

Green Approach toward Sustainable Polymer: Synthesis and Characterization of Poly(myrcene-co-dibutyl itaconate)

Motivated by an epidemic spur in developing sustainable polymers, we report here a series of biobased random rubbery copolymers from β-myrcene and dibutyl itaconate, which have the potential to substitute commercial rubbers. These were prepared by an environmentally benign emulsion polymerization method. The copolymers had predominately 1,4 -cis and -trans-polymyrcene in their microstructure and molecular weight in the range of 13, 330–64, 700 Da. The copolymers displayed a subambient glass transition temperature between −60.3 to −33.5 °C depending on the weight percent of β-myrcene. Morphological studies unveil random placement of the two phases in the copolymer. The copolymers also showed reasonably good thermal stability over the individual homopolymers and pseudoplastic flow behavior. Monitoring of the polymerization reaction at different times and temperatures revealed a first order reaction pathway. A plausible mechanistic insight into the emulsion copolymerization was provided. The reactivity ratio...