Sub-ambient Temperatures Research Articles

A concept for storing utility-scale electrical energy in the form of latent heat

A concept is introduced here for storing utility-scale electrical energy in the form of latent heat. The storage process utilizes a boiling refrigerant at sub-ambient temperatures to freeze a latent heat storage material using electrically driven compressors. Recovery of the latent heat for electrical generation then uses vapor expansion and condensation which essentially reverses the storage process. Sensible heat storage is incorporated into the cycle to efficiently implement the concept. Both energy storage and generation are carried out under steady flow closed-loop conditions where the T-s diagram is similar to a Rankine cycle. From a thermodynamic perspective, work is supplied to the system while heat is transferred to the surroundings from the latent heat store. The reverse process generates work while using heat supplied by the surroundings. An analysis with expander/compressor isentropic efficiencies and small temperature differentials for the heat transfer processes can give projected round trip efficiencies in the 50–60% range using a common refrigerant. One of the attractive features of this approach is the ability to use different ambient temperatures for storage and generation. Exploiting diurnal temperature differences or sources of low grade heat (50–90 °C) significantly increases the apparent round trip storage efficiency.

Thermophysical Properties of Carboxylic and Amino Acid Buffers at Subzero Temperatures: Relevance to Frozen State Stabilization

Macromolecules and other thermolabile biologicals are often buffered and stored in frozen or dried (freeze-dried) state. Crystallization of buffer components in frozen aqueous solutions and the consequent pH shifts were studied in carboxylic (succinic, malic, citric, tartaric acid) and amino acid (glycine, histidine) buffers. Aqueous buffer solutions were cooled from room temperature (RT) to -25 °C and the pH of the solution was measured as a function of temperature. The thermal behavior of frozen solutions was investigated by differential scanning calorimetry (DSC), and the crystallized phases were identified by X-ray diffractometry (XRD). Based on the solubility of the neutral species of each buffer system over a range of temperatures, it was possible to estimate its degree of supersaturation at the subambient temperature of interest. This enabled us to predict its crystallization propensity in frozen systems. The experimental and the predicted rank orderings were in excellent agreement. The malate buffer system was robust with no evidence of buffer component crystallization and hence negligible pH shift. In the citrate and tartrate systems, at initial pH < pK(a)(2), only the most acidic buffer component (neutral form) crystallized on cooling, causing an increase in the freeze-concentrate pH. In glycine buffer solutions, when the initial pH was ∼3 units < isoelectric pH (pI = 5.9), β-glycine crystallization caused a small decrease in pH, while a similar effect but in the opposite direction was observed when the initial pH was ∼3 units > pI. In the histidine buffer system, depending on the initial pH, either histidine or histidine HCl crystallized.

Ethylene separation by feed-splitting from light gases

Separation of ethylene from light gas mixture is one of the most energy intensive separations in petrochemical processes, which uses distillation columns up to 100 m tall and containing over 100 trays due to very small differences in the relative volatilities and very large reflux ratios and also due to the need for sub-ambient temperatures. In recognition of these costs, several attempts have been made in the past to develop processes with less energy and equipment costs. In distillation columns with condenser temperatures significantly below room temperature, such as in ethylene separation towers, it is essential to minimize the expensive energy requirements of the refrigeration cycle that produces the tower reflux. In this work, a solution has been found by expanding the gaseous distillate to decrease its temperature. Moreover, additional solutions applied to conventional ethylene fractionation columns have been implemented here in order to study this behavior. In this contribution, an outlet stream of an Oxidative Coupling of Methane (OCM) reactor, which has been previously stripped of its CO 2 content, is also introduced in a demethanizer tower to remove almost all of its CH 4 content before entering the ethylene fractionating column. Then, it is cooled exchanging its heat with the distillate stream of the ethylene tower, warming the distillate. The main goal is to reduce the condenser heat duty. This objective is achieved reducing a significant amount of heat required by the condenser, maintaining the mandatory product purity. Due to this improvement, it was also possible to reduce the reboiler heat in almost the same percentage amount that is achieved with the condenser. In addition, the reflux of ethylene column decreases. The sensitivity analysis and the corresponding simulations results will be discussed in order to show the efficiency of the presented approach. These results have also been used for the design of the pilot plant which is now being built at our department.

A Mass-Selective Variable-Temperature Drift Tube Ion Mobility-Mass Spectrometer for Temperature Dependent Ion Mobility Studies

A hybrid ion mobility-mass spectrometer (IM-MS) incorporating a variable-temperature (80-400K) drift tube is presented. The instrument utilizes an electron ionization (EI) source for fundamental small molecule studies. Ions are transferred to the IM-MS analyzer stages through a quadrupole, which can operate in either broad transmission or mass-selective mode. Ion beam modulation for the ion mobility experiment is accomplished by an electronic shutter gate. The variable-temperature ion mobility spectrometer consists of a 30.2cm uniform field drift tube enclosed within a thermal envelope. Subambient temperatures down to 80K are achievable through cryogenic cooling with liquid nitrogen, while elevated temperatures can be accessed through resistive heating of the envelope. Mobility separated ions are mass analyzed by an orthogonal time-of-flight (TOF) mass spectrometer. This report describes the technological considerations for operating the instrument at variable temperature, and preliminary results are presented for IM-MS analysis of several small mass ions. Specifically, mobility separations of benzene fragment ions generated by EI are used to illustrate significantly improved (greater than 50%) ion mobility resolution at low temperatures resulting from decreased diffusional broadening. Preliminary results on the separation of long-lived electronic states of Ti(+) formed by EI of TiCl(4) and hydration reactions of Ti(+) with residual water are presented.

Predicting the Crystallization Propensity of Carboxylic Acid Buffers in Frozen Systems—Relevance to Freeze-Drying

Selective crystallization of buffer components in frozen solutions is known to cause pronounced pH shifts. Our objective was to study the crystallization behavior and the consequent pH shift in frozen aqueous carboxylic acid buffers. Aqueous carboxylic acid buffers were cooled to -25°C and the pH of the solution was measured as a function of temperature. The thermal behavior of solutions during freezing and thawing was investigated by differential scanning calorimetry. The crystallized phases in frozen solution were identified by X-ray diffractometry. The malate buffer system was robust with no evidence of buffer component crystallization and hence negligible pH shift. In the citrate and tartarate systems, at initial pH <pKa2 , only the most acidic buffer component (neutral form) crystallized on cooling, causing an increase in the freeze-concentrate pH. Carboxylic acid buffers were rank ordered based on their propensity to crystallize in frozen solutions. From the aqueous solubility values of these carboxylic acids, which have been reported over a range of temperatures, it was also possible to estimate the degree of supersaturation at the subambient temperature of interest. This enabled us to predict their crystallization propensity in frozen systems. The experimental and the predicted rank orderings were in excellent agreement.

Reversed Phase Composite Polymeric Electrolytes Based on Poly(oxyethylene).

In this paper, a concept and structural characterization of novel class of composite polymeric electrolytes is systematically presented. These are polymer-in-ceramic composites consisting of porous alumina matrices, distinguished by different pore architectures (anodized alumina with narrow and well-ordered parallel pores as well as random structures obtained by various methods from alumina grains by sintering); and a complex of lithium tetraoxochlorate and poly(oxyethylene) of different molecular weight. These new electrolytes exhibit room temperature conductivities exceeding 10−3 S·cm−1, low resistance of the interface with lithium electrode, excellent thermal and electrochemical stability. We show combined structural (environmental XRD), thermal and conductivity studies on composite electrolyte systems that were never published before and provide a new explanation of the enhancement of conductivity at subambient temperatures. Feasibility of cells employing electrodes prepared directly on the electrolyt...

F+ and F− Affinities of Simple NxFy and OxFy Compounds

Atomization energies at 0 K and heats of formation at 0 and 298 K are predicted for the neutral and ionic N(x)F(y) and O(x)F(y) systems using coupled cluster theory with single and double excitations and including a perturbative triples correction (CCSD(T)) method with correlation consistent basis sets extrapolated to the complete basis set (CBS) limit. To achieve near chemical accuracy (±1 kcal/mol), three corrections to the electronic energy were added to the frozen core CCSD(T)/CBS binding energies: corrections for core-valence, scalar relativistic, and first order atomic spin-orbit effects. Vibrational zero point energies were computed at the CCSD(T) level of theory where possible. The calculated heats of formation are in good agreement with the available experimental values, except for FOOF because of the neglect of higher order correlation corrections. The F(+) affinity in the N(x)F(y) series increases from N(2) to N(2)F(4) by 63 kcal/mol, while that in the O(2)F(y) series decreases by 18 kcal/mol from O(2) to O(2)F(2). Neither N(2) nor N(2)F(4) is predicted to bind F(-), and N(2)F(2) is a very weak Lewis acid with an F(-) affinity of about 10 kcal/mol for either the cis or trans isomer. The low F(-) affinities of the nitrogen fluorides explain why, in spite of the fact that many stable nitrogen fluoride cations are known, no nitrogen fluoride anions have been isolated so far. For example, the F(-) affinity of NF is predicted to be only 12.5 kcal/mol which explains the numerous experimental failures to prepare NF(2)(-) salts from the well-known strong acid HNF(2). The F(-) affinity of O(2) is predicted to have a small positive value and increases for O(2)F(2) by 23 kcal/mol, indicating that the O(2)F(3)(-) anion might be marginally stable at subambient temperatures. The calculated adiabatic ionization potentials and electron affinities are in good agreement with experiment considering that many of the experimental values are for vertical processes.

Effect of temperature on Mn–Ca selectivity with organophosphorus acid extractants

The effect of temperature on manganese recovery by solvent extraction was studied for the production of high purity MnSO 4 from hydrometallurgical tailings solutions. Two commercially available organophosphorus cation exchange reagents, di-(2-ethylhexyl)phosphoric acid (D2EHPA) and bis(2,4,4-trimethylpentyl)phosphinic acid (CYANEX 272) as the active main components, were chosen. Among these regents, CYANEX 272 is selective for Mn over Ca while D2EHPA is selective for Ca over Mn. CYANEX 272 would therefore be the choice if the aim is to have good Mn/Ca selectivity. It was found, however, that at subambient temperatures the Ca–Mn selectivity of D2EHPA improves remarkably although the extraction order (Ca before Mn) still remains unchanged. As a cheaper reagent D2EHPA would be attractive, but lowering the temperature causes also an increase in viscosity and slower phase separation. The choice in the current case was therefore CYANEX 272 and a temperature of 40 °C. A three-stage Mn extraction followed by two-stage scrubbing and a two-stage sulfuric acid stripping led to a very pure MnSO 4 solution.

Kinetic behaviour in supercritical fluid chromatography with modified mobile phase for 5 μm particle size and varied flow rates

After much development of stationary phase chemistry, in recent years the focus of many studies in HPLC has shifted to increase the efficiency and analysis speed. Ultra high pressure liquid chromatography (UHPLC) using sub-2 μm particles, and high temperature liquid chromatography (HTLC), using temperatures above 100 °C have received much attention. These new approaches allow the use of flow rates higher than those classically used in HPLC, reducing the analysis duration. Due to the low viscosity of supercritical fluids, high velocities, i.e. high flow rates, can be achieved with classical pumping systems typically used in supercritical fluid chromatography (SFC). The effects of the flow rate increase with CO 2/methanol mobile phase was studied on the inlet pressure, t 0, the retention factor of the compounds, and on the efficiency. Simple comparisons of efficiencies obtained at varied temperature between SFC and HPLC, with a packed column containing 5 μm particles, show the greater kinetic performances achieved with the CO 2/methanol fluid, and underline specific behaviours of SFC, occurring for high flow rates and sub-ambient temperature. Some values ( N/ t 0) are also compared to UHPLC data, showing that good performance can be achieved in SFC without applying drastic analytical conditions. Finally, simple kinetic plots ( t 0 vs N) at constant column length are used to select combinations of temperature and flow rate necessary to achieve a required theoretical plate number.

New Semifluorinated Siloxane-Grafted Copolyimides: Synthesis and Comparison with Their Linear Analogs

A siloxane-grafted new diamino monomer DBPDMS has been prepared and used as a co-monomer in combination with the fluorinated diamine monomer TFBB to prepare siloxane-grafted polyimides. The polymers have been characterized by means of GPC, IR, and NMR. Their thermal, mechanical, and surface properties have been evaluated and compared with the homopolyimide and with polyimides where polysiloxane is incorporated in the main chain. DSC revealed melting of the grafted siloxane chain at sub-ambient temperature and a glass transition corresponding to the main polymer chain at high temperature. Isothermal gravimetric analysis at 350 °C indicated that grafted siloxane moiety can be removed thermally from the polymer chain without affecting the polymer backbone.

Development and evaluation of a multiple-plate fraction collector for sample processing: Application to radioprofiling in drug metabolism studies

Microplate scintillation counters are utilized routinely in drug metabolism laboratories for the off-line radioanalysis of fractions collected during HPLC radioprofiling. In this process, the current fraction collection technology is limited by the number of plates that can be used per injection as well as the potential for sample loss due to dripping or spraying as the fraction collector head moves from well to well or between plates. More importantly, sample throughput is limited in the conventional process, since the collection plates must be manually exchanged after each injection. The Collect PAL, an innovative multiple-plate fraction collector, was developed to address these deficiencies and improve overall sample throughput. It employs a zero-loss design and has sub-ambient temperature control. Operation of the system is completely controlled with software and up to 24 (96- or 384-well) fraction collection plates can be loaded in a completely automated run. The system may also be configured for collection into various-sized tubes or vials. At flow rates of 0.5 or 1.0 mL/min and at collection times of 10 or 15 s, the system precisely delivered 83-μL fractions (within 4.1% CV) and 250-μL fractions (within 1.4% CV), respectively, of three different mobile phases into 12 mm × 32 mm vials. Similarly, at a flow rate of 1 mL/min and 10 s collection times, the system precisely dispensed mobile phase containing a [ 14C]-radiolabeled compound across an entire 96-well plate (% CV was within 5.3%). Triplicate analyses of metabolism test samples containing [ 14C]buspirone and its metabolites, derived from three different matrices (plasma, urine and bile), indicated that the Collect PAL produced radioprofiles that were reproducible and comparable to the current technology; the % CV for 9 selected peaks in the radioprofiles generated with the Collect PAL were within 9.3%. Radioprofiles generated by collecting into 96- and 384-well plates were qualitatively comparable; however, the peak resolution was greater in the profiles that were collected in 384-well plates due to the collection of a larger number of fractions per minute. In conclusion, this new and innovative fraction collector generated radioprofile results that were comparable to current technology and should provide a major improvement in capacity and throughput for radioprofiling studies.

Analysis of UV ink photoinitiators in packaged food by fast liquid chromatography at sub-ambient temperature coupled to tandem mass spectrometry

A fast method of liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS) was developed for the analysis of eleven UV ink photoinitiators in packaged food. Chromatographic separation was achieved in a pentafluorophenylpropyl (PFPP) column at 5°C and acetonitrile:25mM formic acid–ammonium formate (pH 2.7) in gradient elution. To reduce sample treatment, a QuEChERS (quick, easy, cheap, effective, rugged and safe) method for the extraction and clean-up of UV photoinitiators in packaged foods was evaluated. Triple quadrupole working in H-SRM on Q1 mode was used for both quantitation and confirmation purposes and the most intense and selective transitions were chosen. Quality parameters of the developed QuEChERS LC–MS/MS method were established and applied for the analysis of photoinitiators in food packaged at ngkg−1 levels.

Solid-State Refrigeration Based on the Electrocaloric Effect for Electronics Cooling

Subambient temperature operations of advanced semiconductor devices offer many benefits, including improved reliability, reduced leakage currents, and enhanced signal to noise ratios. We discuss a new design concept for compact solid-state refrigerators based on the electrocaloric (EC) effect. The EC refrigerators are attractive because they may approach the Carnot efficiency more closely than Peltier coolers, which involve intrinsically irreversible processes. To address parasitic losses and other practical considerations that limit the actual performance of EC coolers, we incorporate laterally interdigitated electrode arrays with high effective thermal conductivity and switchable thermal interfaces with high switching ratios and high off-state thermal resistance. Numerical simulations are used to quantify the impact of various design parameters and the expected performance of the module, focusing in particular on the heat diffusion time and RC thermal time constant. Based on the material properties reported in the literature, we project that cooling power densities &gt;10 W/cm2 may be achieved across ΔT of the order of 10 K at coefficient of performance (COP)&gt;10. The present work motivates further experimental studies to develop advanced electrocaloric materials and fabricate/test cooling modules to assess the feasibility of their practical application.

Generation of electricity in microbial fuel cells at sub-ambient temperatures

Direct generation of electricity from a mixture of carbon sources was examined using single chamber mediator-less air cathode microbial fuel cells (MFCs) at sub-ambient temperatures. Electricity was directly generated from a carbon source mixture of d-glucose, d-galactose, d-xylose, d-glucuronic acid and sodium acetate at 30°C and <20°C (down to 4°C). Anodic biofilms enriched at different temperatures using carbon source mixtures were examined using epi-fluorescent, scanning electron microscopy, and cyclic voltammetry for electrochemical evaluation. The maximum power density obtained at different temperatures ranged from 486±68mWm−2 to 602±38mWm−2 at current density range of 0.31mAcm−2 to 0.41mAcm−2 (14°C and 30°C, respectively). Coulombic efficiency increased with decreasing temperature, and ranged from 24±3 to 38±1% (20°C and 4°C, respectively). Chemical oxygen demand (COD) removal was over 68% for all carbon sources tested. Our results demonstrate adaptation, by gradual increase of cold-stress, to electricity production in MFCs at sub-ambient temperatures.

A study of low temperature mechanical properties and creep behaviour of polypropylene using a new sub-ambient temperature nanoindentation test platform

Mechanical properties and creep behaviour of an atactic-polypropylene (aPP) have been studied in the vicinity of its glass transition temperature (−18 °C) via a nanoindentation platform integrated with a sub-ambient temperature capability. All low temperature tests were validated by measurements on a fused silica reference sample from 25 to −30 °C. The fused silica results showed virtually invariant elastic modulus with temperature over this range consistent with the literature measurements by sonic resonance. Hardness and elastic modulus of aPP increased as the test temperature decreased and the amorphous regions went through the glass transition. The creep behaviour was analysed using two approaches: (i) a logarithmic method and (ii) the Boltzmann integral method. The results showed that the creep extent decreased as the temperature was reduced, and for the time constants obtained there were upper-limit values at −10 °C, about 8 °C above the quoted glass transition temperature. The strain rate sensitivity obtained by the logarithmic method also showed a maximum at −10 °C.

Analysis of Refrigeration Requirements of Digital Processors in Subambient Temperatures

The total power consumption for high-performance computing systems is a serious concern for designers of integrated circuits and systems. It is well known that cooling the operating temperature results in reduced electronic power and/or speed gains. However, total power dissipation includes both electronic power and the refrigeration power. This study explores the optimal operating temperatures and the amount of total power reduction at subambient temperatures. This paper presents a realistic system-level model that includes both the electronic and the refrigeration systems. Analysis using the model shows the optimal temperature, and sensitivity to parameters of the electronic and refrigeration systems. For instance, a system with 50% electronic leakage and a minimum refrigeration coefficient of performance (COP) of 3.3, the optimized design operates at 8°C and offers a 44% power reduction over the noncooled design. Analysis also shows that temperatures near that of domestic freezers is nearly optimal for digital processors and such cooling may be viable approach for current and future electronics due to the scaling trends of integrated circuits technology.

NMR and dielectric studies of hydrated collagen and elastin: Evidence for a delocalized secondary relaxation

Using a combination of dielectric spectroscopy and solid-state deuteron NMR, the hydration water dynamics of connective tissue proteins is studied at sub-ambient temperatures. In this range, the water dynamics follows an Arrhenius law. A scaling analysis of dielectric losses, ‘two-phase’ NMR spectra, and spin-lattice relaxation times consistently yield evidence for a Gaussian distribution of energy barriers. With the dielectric data as input, random-walk simulations of a large-angle, water reorientation provide an approximate description of stimulated-echo data on hydrated elastin. This secondary process is quasi-isotropic and delocalized. The delocalization is inferred from previous NMR diffusometry experiments. It is emphasized that the phenomenology of this process is shared by many non-aqueous binary glasses in which the constituent components exhibit a sufficient dynamical contrast.

ChemInform Abstract: Substituent Effects in the Gas Phase: 1-Substituted Allyl Anions

A series of 1-substituted allyl anions containing first-row, second-row, and resonance-stabilizing substituents has been examined in the gas phase with a variable-temperature flowing afterglow device. Several of these ions are weakly bound, undergo electron detachment readily, and can only be studied at subambient temperatures. The reactivity and thermodynamic properties of these species are reported. 3-Fluoropropene, 3-methoxypropene, 3-(dimethylamino)propane, and propene all have identical acidities. Electron-withdrawing and π-donating substituents (F, OCH 3 , and N(CH 3 ) 2 ) do not destabilize allyl anion by increasing its basicity but rather by decreasing its electron-binding energy. There is, however, a linear correlation between acidity and electron affinity. Ab initio calculations reveal that the geometries of the allylic anions vary considerably as a result of a number of compensating factors, including inductive, resonance, and polarization effects. Consequently, linear free energy relationships are not applicable, and different substrates may respond to the same substituents in very different ways

Properties of new low melting point quaternary ammonium salts with bis(trifluoromethanesulfonyl)imide anion

Eight new monocationic quaternary ammonium (QA) salts with the bis(trifluoromethanesulfonyl)imide (TFSI) anion were prepared by metathesis using our previously reported QA halides as precursors. New salts were characterized both in liquid and solid state using 1H and 13C NMR techniques, mass spectroscopy and elemental analysis together with X-ray diffraction and thermoanalytical methods. In addition, residual water content, viscosity and conductivity measurements were made for three of the room-temperature ionic liquids (RTILs). The crystal structures of three compounds were determined by X-ray single crystal diffraction. Powder diffraction was used to study the crystallinity of the solid salts and to compare structural similarities between the single crystals and the microcrystalline bulk powders. Three of the salts are liquid below room temperature, having broad liquid ranges (∼300 °C), and in total five out of eight salts melt below 100 °C. Moreover, powder diffraction data of the two RTILs were able to be measured at sub-ambient temperatures using in situ low-temperature powder X-ray diffraction revealing high crystallinity on both RTILs below their freezing point. The RTILs presented relatively high conductivities (∼0.1–0.2 S m −1) and moderate to relatively low viscosities. The determined physicochemical properties of the reported ILs suggest their applicability on various applications such as heat transfer fluids, high temperature synthesis and lubricants.

ChemInform Abstract: Dimethyldioxirane Epoxidation of Enol Phosphates.

Abstract The novel epoxides 2 of a variety of enol phosphates 1 were readily prepared by epoxidation with dimethyldioxirane at subambient temperatures; at room temperature these labile epoxides 2 rearranged into the corresponding α-dialkoxyphosphinyloxy-substituted carbonyl products 3.