A new analytical modeling for the determination of thermodynamic quantities of refrigerants

A new analytical fundamental equation of state (EOS) is presented for fluids. The equation is explicit in the effective molecular potentials and allows calculation of all thermodynamic properties over the whole fluid surface (gas, liquid, supercritical and gas–liquid phase transition). Outside the critical area (± 0.05T_c), it is valid in a vast range of temperature and pressure (0.8T_c to 7.5T_c and up to 120P_c,). The EOS is applicable for a variety of refrigerants such as C₃H₂F₄ (HFO-1234ze (E)), hydrofluorocarbons (HFCs) including C₃F₈ (R218), C₃H₂F₆ (R236ea), C₃H₂F₆ (R236fa), C₃H₃F₅ (R245ca), C₃HF₇, C₄F₈ (RC318), C₄F₁₀, C₅F₁₂, natural refrigerants including NH₃, CO₂, hydrocarbons, monatomic gases and some other fluids. Calculations of second derivatives properties of fluids are sensitive tests of EOS behavior. Therefore, estimation of the thermodynamic properties including Joule-Thomson coefficient, μ_JT, and speed of sound, w, has been considered.     

Power generation from waste heat: Ionic liquid-based absorption cycle versus organic Rankine cycle

Aspen Plus® simulations using the Peng-Robinson (PR-EOS) and the COSMO-SAC models were performed to study absorption power cycles (APCs) using mixtures of R-134a with two ionic liquids, [C₂C₁im][Tf₂N] or [C₆C₁im][Tf₂N], and compared against an R-134a organic Rankine cycle (ORC) operating under similar conditions. The PR-EOS results were in agreement with calculations from a PR model fitted to the R-134a + IL experimental phase equilibrium data. The APCs have similar efficiencies and outperform the ORC by 3%–46%, with the largest differences observed when operating with lower grade (lower T_H) heating sources, lower quality cooling (higher T_L), and lower subcooling in the pump inlet stream. The PR-EOS and the Conductor-like Screening Model Segment Activity Coefficient (COSMO-SAC) results follow similar trends, but numerical discrepancies are observed in the cycle efficiencies and stream flow rates and compositions due to differences in solubilities and enthalpy changes between both models, suggesting that improvements are needed to increase the accuracy of COSMO-SAC for these systems.     

Carbosilane Metallodendrimers with Cyclopentadienyldichlorotitanium(IV) End Groups

Dendritic polyols of the second and third generation 2G-OH₈ (1), 2G-OH₁₆ (2), and 3G-OH₁₆ (3) were prepared by hydroboration/oxidation of allyl-terminated carbosilane dendrimers and used as supports for the immobilization of cyclopentadienyltrichlorotitanium(IV) complexes via alcoholysis. The reaction of 1–3 with CpTiCl₃ gave metallodendrimers 2G-(OTiCpCl₂)₈ (4a), 2G-(OTiCpCl₂)₁₆ (5a), and 3G-(OTiCpCl₂)₁₆ (6a), respectively, whereas the reaction of 1 and 3 with CpSi^FTiCl₃ (CpSi^F = C₅H₄SiMe₂CH₂CH₂C₈F₁₇) yielded peripherally fluorinated metallodendrimers 2G-(OTiCpSi^FCl₂)₈ (4b) and 3G-(OTiCpSi^FCl₂)₁₆ (6b). All metallodendrimers were characterized by multinuclear NMR spectroscopy. The suggested structures were supported by comparison with model 1-propoxycomplexes 10a,b. To identify side products of the alcoholysis reaction, hydrolytic behavior of the starting trichloro complexes was studied both in solid state and in solution. The main products of hydrolysis in solution were identified as μ-oxocomplexes 8a,b whereas hydrolysis in solid state yielded mainly hydroxycomplexes 7a,b.     

Structural and physicochemical studies of hydration of crosslinked TBA polyacrylates with different substitution degrees of H+ ions with TBA+ ions

X‐ray powder diffraction studies and physicochemical studies have been carried out of the hydrate phases formed in binary water systems with crosslinked tetrabutylammonium (TBA) polyacrylates (n = 1%) in mixed [x(C₄H₉)₄N + (100?x)H] form with low degrees of substitution of proton ions of the carboxylic groups in poly(acrylic acid) for TBA cations x = 40%, 30%, and 20%. As was shown by structural studies, the clathrate hydrate is formed in the water system with the polyacrylate in the mixed form with x = 40%. The structure is analogous to that of earlier studied hydrates formed by crosslinked polyacrylates in mixed [x(C₄H₉)₄N + (100?x)H] form with higher values of x = ～100%, 80%, and 60% and can be related to the tetragonal structure I, characteristic of the ionic clathrate hydrates of TBA salts with monomeric anions. Decomposition temperature and fusion enthalpy of the studied hydrate were determined using differential thermal analysis and calorimetric methods. It was revealed that the further decrease of x led to the destruction of clathrate hydrate framework. According to the results of X‐ray powder diffraction research, the phase of ice is crystallized instead of the hydrate phase in water systems with the polyacrylates with x = 30% and 20%. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46209.     

Decomposition kinetics and recycle of binary hydrogen‐tetrahydrofuran clathrate hydrate

Decomposition kinetics and recycle of hydrogen–tetrahydrofuran (H₂–THF) clathrate hydrates were investigated with a pressure decay method at temperatures from 265.1 to 273.2 K, at initial pressures from 3.1 to 8.0 MPa, and at stoichiometric THF hydrate concentrations for particle sizes between 250 and 1000 μm. The decomposition was modeled as a two‐step process consisting of H₂ diffusion in the hydrate phase and desorption from the hydrate cage. The adsorption process occurred at roughly two to three times faster than the desorption process, whereas the diffusion process during formation was slightly higher (ca. 20%) than that during decomposition. Successive formation and decomposition cycles showed that occupancy seemed to decrease only slightly with cycling and that there were no large changes in hydrate structure due to cycling. Results provide evidence that the formation and decomposition of H₂ clathrate hydrates occur reversibly and that H₂ clathrate hydrates can be recycled with pressure. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Effects of Graphene Oxide Nanosheets and Al2O3 Nanoparticles on CO2 Uptake in Semi‐clathrate Hydrates

Gas hydrate/clathrate hydrate formation is an innovative method to trap CO₂ into hydrate cages under appropriate thermodynamic and/or kinetic conditions. Due to their excellent surface properties, nanoparticles can be utilized as hydrate kinetic promoters. Here, the kinetics of the CO₂ + tetra‐n‐butyl ammonium bromide (TBAB) semi‐clathrate hydrates system in the presence of two distinct nanofluid suspensions containing graphene oxide (GO) nanosheets and Al₂O₃ nanoparticles is evaluated. The results reveal that the kinetics of hydrate formation is inhibited by increasing the weight fraction of TBAB in aqueous solution. GO and Al₂O₃ are the most effective kinetic promoters for hydrates of (CO₂ + TBAB). Furthermore, the aqueous solutions of TBAB + GO or Al₂O₃ noticeably increase the storage capacity compared to TBAB aqueous solution systems.     

Influence of water activity on hydration of tricalcium aluminate-calcium sulfate systems

The hydration of tricalcium silicate (C₃S)—the major phase in cement—is effectively arrested when the activity of water (a_H) decreases below the critical value of 0.70. While it is implicitly understood that the reduction in a_H suppresses the hydration of tricalcium aluminate (C₃A: the most reactive phase in cement), the dependence of kinetics of C₃A hydration on a_H and the critical a_H at which hydration of C₃A is arrested are not known. This study employs isothermal microcalorimetry and complementary material characterization techniques to elucidate the influence of a_H on the hydration of C₃A in [C₃A + calcium sulfate (C$) + water] pastes. Reductions in water activity are achieved by partially replacing the water in the pastes with isopropanol. The results show that with decreasing a_H, the kinetics of all reactions associated with C₃A (eg, with C$, resulting in ettringite formation; and with ettringite, resulting in monosulfoaluminate formation) are proportionately suppressed. When a_H ≤0.45, the hydration of C₃A and the precipitation of all resultant hydrates are arrested; even in liquid saturated systems. In addition to—and separate from—the experiments, a thermodynamic analysis also indicates that the hydration of C₃A does not commence or advance when a_H ≤0.45. On the basis of this critical a_H, the solubility product of C₃A (K_C3A) was estimated as 10^−20.65. The outcomes of this work articulate the dependency of C₃A hydration and its kinetics on water activity, and establish—for the first time—significant thermodynamic parameters (ie, critical a_H and K_C3A) that are prerequisites for numerical modeling of C₃A hydration.     

Effects of promoter and moisture on the deactivation of FSO<Subscript>3</Subscript>H catalyst in the synthesis of HFC-152a by hydrofluorination of acetylene

The effects of promoter type and moisture on the catalytic activity of fluorosulfonic acid (FSO₃H) as a liquid catalyst for the synthesis of HFC-152a by the hydrofluorination of acetylene were investigated. The catalyst containing SnCl₄ as a promoter had a long catalyst lifetime compared to that without any promoter. It was also found that the composition of HFC-152a can be maintained at 100% for a long time by the control of the moisture content.     

STUDY OF CLATHRATE HYDRATION OF CARBOXYLIC ION EXCHANGER BY DTA METHOD

ABSTRACT

The effect of ionic composition [(C₄H₉) ₄N-, H + (C₄H₉)N- and H-forms] and degree of swelling of a polyacrylic ion exchanger on the formation and stability of crystalline clathrate hydrates is studied. The melting temperature of clathrates for ion exchanger in the mixed ion form is to a large extent determined by the ratio of counter-ions. For the first time discovered the clathrate-formation for H-forms of carboxylic ion exchanger. Shown that crystalline inclusion compounds an clathrate type for ion exchangers on structure are related to tetragonal type (TS-1).     

Chemical transformations of functional polycarbosilanes

The functional polycarbosilane [Si(X ₂)C₂H₄] _n , whereX ₂=Cl₂ (1), was chemically transformed into the corresponding polymers, whereX ₂=F₂ (3), (2-N, N-dimethylbenzylamino)(H) (5), (9-N,N-dimethyl-1-naphthylamino)(H) (6), (1-C₁₀H₇)(H) (7), Me₂ (8a), (Me₃SiNH)₂ (10), and (vinyl)(H) (11). The functional polycarbosilane, whereX ₂=H₂ (2), was converted into the polymers, whereX ₂=Me(H) (8b) and (OMe)₂ (9). Reaction of3 with KF in the presence of 18-crown-6 gave rise to the poycarbosilane4 containing both pentacoordinate and tetracoordinate silicons in the proportion of 1:15 as shown by quantitative¹⁹F and²⁹Si NMR. Conversion of a greater proportion of silicon atoms to the pentacoordinate state was not possible because of insolubility of the resulting ionomer in the reaction medium.     

Structural Transition of the 2‐Nitropropane Organic Compound at Low Temperature

Structural investigation of the crystallized 2‐nitropropane compound (C₃H₇NO₂) was performed by X‐ray powder diffraction at low temperature. A first crystalline phase, called phase α, is observed below 172 K. This form exhibits a triclinic symmetry with P‐1 space group (a=1.0313(3) nm, b=0.5873(2) nm, c=1.6146(4) nm, α=90.17(2)°, β=92.17(2)° and γ=90.09(2)°), and Z=8). At T_t=172 K, a structural transition is observed which brings to another phase, called phase β (above T_t). This one contains four molecules per unit cell and shows a Pc2₁n symmetry (a=1.0141(3) nm, b=0.5855(2) nm, and c=0.8319(4) nm). In addition to the doubling of the c‐axis, structural networks differ by the different conformations of NO₂ nitro groups and by the orientation of the propyl group in the unit cell. Both crystal structures can be described using infinite zigzag chains of C₃H₇NO₂ molecules showing a regular alternation along the c‐axis. Two orientations of these ribbons, called A and B, are observed. The crystal structures are then built with different distribution of these ribbons within the crystalline network.     

Enclathration of hydrogen by organic-compound clathrate hydrates

The properties of hydrogen enclathration by cyclic ethers and acetone clathrate hydrates were investigated by powder X-ray diffraction, Raman spectroscopic analysis and volumetric analysis. Powder X-ray diffraction profiles indicate that the hydrates are structure-II hydrates. The variation in lattice constant by hydrogen occupation was investigated. This result indicates that inclusion of H₂ atom within empty small cage changes size of host cages depending on type of guest molecule. Raman results show that the samples formed binary clathrate hydrate of hydrogen and each organic compound. The amount of encaged H₂ was found to be comparable to that of H₂–THF binary hydrate. The trend of the changes for lattice constants is not related to the amount of encaged H₂. These results suggest that the organic compounds investigated in this study can be used as alternatives to THF for H₂ enclathration.     

Die swell of liquid crystal-forming solutions of hydroxypropyl cellulose through a long capillary die

The die swell and shear viscosity of lyotropic liquid crystal-forming hydroxypropyl cellulose solutions in N,N-dimethylacetamide were determined over a relatively wide range of shear stress or polymer concentration at 30°C by using a long capillary die with an aspect ratio of 114. The dependence of die swell on the concentration was similar to that of shear viscosity: a maximum at a critical concentration C_a and a minimum at another critical concentration C_b (C_a < C_b). The dependence of the swell on shear stress is greatly affected by the solution phase: in an isotropic range (below C_a), the die swell increased monotonously with shear; in the vicinity of C_a, the die swell exhibited a maximum; in a biphasic range (between C_a and C_b), the die swell decreased monotonously; in a single-phase anisotropic range (above C_b), the die swell exhibited a minimum. Above C_b, extrudate distortion was observed and disappeared around the shear where the die swell exhibited a minimum.     

High-pressure NMR studies of the water soluble rhodium hydroformylation system

Rh(CO)₂(acac) reacts with P(m-C₆H₄SO₃Na.H₂O)₃ (P/Rh > 3.5) in water under CO to give HRh(CO)[P(m-C₆H₄SO₃Na)₃]₃ (1a), the structure of which is similar to HRh(CO) (PPh₃)₃ (1b). High pressure NMR spectra of an aqueous solution containing1a and three molar excess of P(m-C₆H₄SO₃Na)₃ does not show the formation of new species up to 200 atm of COH₂(11). In contrast,1b, in the presence of three molar excess of PPh₃, is completely converted to HRh(CO)₂(PPh₃)₂ (2b) under 30 atm CO/H₂(11) in toluene. The activation energy of the dissociation of P(m-C₆H₄SO₃Na)₃ from1a in water was found to be 30±1 kcal/mol, which is 11±1 kcal/mol higher than the dissociation of PPh₃ from1b in toluene.     

Solubility measurement of hydrogen,ethylene, and 1‐hexene in polyethylene films through an intelligent gravimetric analyzer

The solubility of hydrogen (H₂), ethylene (C₂H₄), 1‐hexene (C₆H₁₂), and the mixture of C₂H₄/1‐C₆H₁₂ in semicrystalline polyethylene (PE) films is measured using an intelligent gravimetric analyzer (IGA) in combination with prediction equations. For the pure‐component sorption in PE, the solubility of C₂H₄ and 1‐C₆H₁₂ decreases with the temperature, while that of H₂ exhibits an opposite variation tendency in the temperature range under test. For the C₂H₄/1‐C₆H₁₂ mixture, the co‐solubility is almost 10% smaller than the sum of the pure‐component solubility. 1‐C₆H₁₂ acts as a co‐solvent and C₂H₄ an antisolvent. Moreover, good consistency has been achieved between the measured data and the prediction results from the Sanchez‐Lacombe EOS model, demonstrating the reliability of the measurement approach employed in this work. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44507.     

Synthesis of fluorocyclohexadienes by the electrochemical fluorination of p-difluorobenzenes on a preparative scale

Fluorine containing-cyclohexadienes (FCHDs), 3,3,6,6,-tetrafluoro-1,4-cyclohexadiene (1a), 1-chloro-3,3,6,6-tetrafluoro-1,4-cyclohexadiene (3a) and 1-bromo-3,3,6,6-tetrafluoro-1,4-cyclohexadiene (4a), were isolated in pure states with high yields (ca. 80%) by the preparative scale electrochemical fluorination of 1,4-difluorobenzene (1), 1-chloro-2,5-difluorobenzene (3) and 1-bromo-2,5-difluorobenzene (4), respectively, in Et₄NF · mHF (Et = C₂H₅: m = 4.0, 4.45 and 4.7) at a platinum anode, followed by extraction and fractional distillation. The electrochemical fluorination of 1,2,4-trifluorobenzene (2) yielded both 1,3,3,6,6-pentafluoro-1,4-cyclohexadiene (2a) and 2,5,5,6,6-pentafluoro-1,3-cyclohexadiene (2b) with high yield (ca. 90%). Some of (2a) was also isolated in a pure state by fractional distillation. Each substrate compound (1–4) was fluorinated to the corresponding FCHDs with an almost quantitative yield when 2.0–2.1 faraday (per mol of substrate) of electricity was passed.     

One pot solvent-free synthesis of 2H-pyrano, 2H-thiopyrano, 2H-selenopyrano[2,3-b]-1,8-naphthyridin-2-ones on solid phase catalyst under microwave irradiation

A simple and efficient procedure has been developed for the synthesis of the 2H-pyrano (3a–c), 2H-thiopyrano (5a–c), 2H-selenopyrano[2,3-b]-1,8-naphthyridin-2-ones (7a–c) by cyclisation of 2-chloro-3-formyl[1,8]naphthyridines (1a–c) with acetic anhydride under microwave irradiation using solid phase catalyst anhydrous sodium acetate. These new compounds were characterized by elemental analysis, IR, ¹H NMR and mass spectral studies.     

Solubilization of Ni Imidazole Complex in Micellar Media of Anionic Surfactants,Sodium Dodecyl Sulfate and Sodium Stearate

The solubilization and physicochemical behavior of a coordination complex of nickel, namely [Ni(im)₆]F₂·5H₂O [hexakis(imidazole)nickel(II) fluoride pentahydrate], in aqueous micellar media of anionic surfactants, i.e., sodium dodecyl sulfate (SDS) and sodium stearate (SS), were investigated by using UV–Vis spectroscopy and electrical conductivity measurements. Spectroscopic techniques were used for the computation of binding constant (K_b), partition coefficient (K_x), change in free energy of binding (ΔG_b), and change in free energy of partition (ΔG_p), whereas electrical conductivity data was helpful to calculate thermodynamic parameters of micellization of surfactants in the presence of the Ni complex, i.e., standard entropy of micellization (ΔS_m), free energy (ΔG_m), and enthalpy of micellization (ΔH_m). It is evident from the results that solubilization of the Ni complex takes place because of electrostatic as well as hydrophobic interactions. The presence of the Ni complex in micellar media increases the critical micelle concentration of both surfactants owing to the structure‐breaking effect.     

Selective ethylene‐permeable zeolite composite double‐layered film for novel modified atmosphere packaging

The composite double‐layered films, for the packaging application of postharvest fruits and vegetables, were prepared by laminating low‐density polyethylene (LDPE) and poly[styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene] (SEBS) modified with zeolite ZSM‐5. The film was characterized by scanning electron microscope and differential scanning calorimeter and tested for permeation of ethylene (C₂H₄), oxygen (O₂), carbon dioxide (CO₂), and water vapor. It was found that the C₂H₄ permeability of the films was improved because of an enhanced adsorption of C₂H₄ by the incorporated zeolite (0–10 wt%). The preconcentrated layer (zeolite/SEBS) leads to a higher C₂H₄ concentration gradient across the film. Moreover, the high dispersion of zeolite increased the C₂H₄ permeation. When compared with O₂ and CO₂, the composite films were more selective to C₂H₄. However, the C₂H₄ permeation decreased in the presence of O₂ because of a competitive adsorption. In addition, the films possessed appreciate tensile properties for packaging application. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Titanium complexes with β-ketoiminate chelate ligands for ethylene polymerization: The significant influence of substituents on structures and catalytic activities

Four titanium complexes having β-ketoiminate chelate ligands with fluorine or alkyl groups [(Ar)NC(CH₃)C(H)C(CH₃)O]₂TiCl₂ (3a: Ar = 2.6-F₂C₆H₃; 3b: Ar = C₆F₅; 3c: Ar = 2.6-Me₂C₆H₃; 3d: Ar = 2.6-ⁱPr₂C₆H₃) have been synthesized and characterized by ¹H NMR and EA. Complexes 3a, 3c and 3d were further characterized by X-ray diffraction analysis and demonstrated distorted octahedral coordination structure around the titanium center. The substituents in ligands greatly affect the coordination mode, resulting in three different isomeric structures. These complexes are active catalysts for polymerization of ethylene with MMAO as cocatalyst. The substituents in ligands have also great influences on catalytic activity. The complexes with alkyl groups have lower activity, while the complexes with fluorine atoms have middle or high catalytic activity.