Experimental determination of concentration dependence of nitrogen diffusivity in polypropylene

This study determines the diffusivity of nitrogen as a function of its concentration in polypropylene at 170, 180, and 190°C in the range, 0.99–6.75 MPa. Isothermal pressure decay experiments are utilized to obtain the uptake of nitrogen by polypropylene with time. These data when used with a detailed mass transfer model, and the principles of variational calculus allow the determination of the nitrogen diffusivity. It is found to be a peak function with values in the range of 3.88 × 10^?9 to 12.94 × 10^?9 m² s^?1. Suitable correlations are found to represent the diffusivity in terms of pressure and nitrogen concentration at the three temperatures. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Characterization of temperature‐dependent moisture diffusivity in PMR‐15 resin

The temperature‐dependent moisture diffusion behavior of high‐temperature polyimide resin, PMR‐15, is presented. Adsorption and high temperature desorption tests are used to experimentally determine moisture diffusivity at several temperatures. Diffusivity is determined from the weight change based on the initial slope and using a nonlinear regression technique with Fickian diffusion assumption. The basic test procedures and diffusivity values are presented in this study. The results also include the relative humidity (RH) dependent equilibrium moisture concentration and a relationship between the RH and equilibrium moisture concentration. As direct measurement at typical operating temperature may be precluded by blistering, an Arrhenius‐type temperature‐diffusivity relationship is used to estimate the temperature‐dependent moisture diffusivity for the PMR‐15 resin. The moisture diffusivity of PMR‐15 tested is estimated to be 6.64 E ?10 m²/s at 288°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Preparation of polyethylene‐octene elastomer/clay nanocomposite and microcellular foam processed in supercritical carbon dioxide

Polyethylene‐octene elastomer (POE)/organoclay nanocomposite was prepared by melt mixing of the POE with an organoclay (Cloisite 20A) in an internal mixer, using poly[ethylene‐co‐(methyl acrylate)‐co‐(glycidyl methacrylate)] copolymer (E‐MG‐GMA) as a compatibilizer. X‐ray diffraction and transmission electron microscopy analysis revealed that an intercalated nanocomposite was formed and the silicate layers of the clay were uniformly dispersed at a nanometre scale in the POE matrix. The nanocomposite exhibited greatly enhanced tensile and dynamic mechanical properties compared with the POE/clay composite without the compatibilizer. The POE/E‐MA‐GMA/clay nanocomposite was used to produce foams by a batch process in an autoclave, with supercritical carbon dioxide as a foaming agent. The nanocomposite produced a microcellular foam with average cell size as small as 3.4 µm and cell density as high as 2 × 10¹¹ cells cm^?3. Copyright © 2005 Society of Chemical Industry     

超临界二氧化碳发泡EPDM/LDPE热塑性弹性体微孔泡沫

本文通过熔融共混制得了EPDM/LDPE热塑性弹性体,压制标准试样,然后使用超临界二氧化碳作为发泡剂在高压反应釜中进行物理发泡。通过万能拉力机测试了弹性体力学性能,用扫描电镜观察了拉伸断面和泡孔的微观结构。结果表明：DCP硫化体系的热塑性弹性体的综合力学性能要优于硫黄硫化体系,随着硫化剂用量的增多,拉伸强度和撕裂强度有一个最大值,硬度上升;橡塑比在4:6时,力学性能达到最佳,最大拉伸强度为7.5MPa,最大撕裂强度为27.6MPa。扫描电镜观察其拉伸断面形貌,表明EPDM橡胶相与LDPE塑料相呈现“海-岛”两相微观结构;泡孔大小均匀性较好,成功制备了微米级微孔泡沫且泡孔大小分布均匀。     

Supercritical carbon dioxide extraction in membrane formation by thermally induced phase separation

In this study, a novel and environmentally friendly extracting method, supercritical carbon dioxide (SC‐CO₂) extraction, was investigated in the thermally induced phase separation (TIPS) process for making microporous membranes. In the SC‐CO₂ extraction, the effects of extraction time, pressure, and temperature on the extraction fraction, membrane morphology, and membrane performance were investigated. It was concluded that with extraction conditions of 18 MPa, 35°C and 2 h, the porous membrane had the highest extraction fraction. There was a close relationship between membrane performance and the extraction conditions of SC‐CO₂, and it is possible to tailor membrane performance through the choice of extraction conditions. Compared with traditional solvent extraction, a dry membrane treated by SC‐CO₂ extraction has much less shrinkage and greater water permeability, whereas the degree of crystallization of a membrane extracted by SC‐CO₂ is slightly greater than that extracted by ethanol. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1632–1639, 2007     

Time dependences of conduction and self‐heating in acetylene carbon black‐filled high‐density polyethylene composites

The time dependences of electrical conduction and self‐heating behaviors in high‐density polyethylene filled with acetylene carbon black of 0.082 in volume fraction are studied in relation to voltage and ambient temperature. The characteristic decay current constant τ_i, and the exponential growth time constant for self‐heating τ_g are determined for the samples under voltages U above the critical value U_c for the onset of self‐heating. The influences of voltage and ambient temperature on τ_i and τ_g as well as the amplitude of the low‐resistance to high‐resistance switching are discussed on the basis of the random resistor network (RRN) model and the relationship between U_c and the intrinsic resistivity. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1124–1131, 2006     

Prediction of mass diffusivity of CO2 into bitumen

The infinite dilution and mutual diffusion coefficients for the CO₂/bitumen system were predicted using existing correlations. Out of seven semi-empirical correlations tested, the Umesi-Danner correlation was found to be best suited for the prediction of gas-liquid infinite dilution diffusion coefficient. For the mutual diffusion coefficient, Teja's method based on the generalized corresponding states principle was successfully used. The predictions are compared with the limited CO₂/bitumen diffusivity data available in the literature.     

The effect of a concentration‐dependent viscosity on particle transport in a channel flow with porous walls

The transport of a dilute suspension of particles through a channel with porous walls, accounting for the concentration dependence of the viscosity, is analyzed. In particular, we study two cases of fluid permeation through the porous channel walls: (1) at a constant flux and (2) dependent on the pressure drop across the wall. We also consider the effect of mixing the suspension first compared with point injection by considering inlet concentration distributions of different widths. We find that a pessimal inlet distribution width exists that maximizes the required hydrodynamic pressure for a constant fluid influx. The effect of an external hydrodynamic pressure, to compensate for the reduced transmembrane pressure difference due to osmotic pressure, is investigated. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1891–1904, 2014     

Oxygen and carbon dioxide permeability of EAA/PEO blends and microlayers

The goal of this study was to broaden the spectrum of gas permeability and selectivity characteristics of poly(ethylene‐co‐acrylic acid) (EAA) by combining it with poly(ethylene oxide) (PEO), which has a high selectivity for CO₂. To obtain films that differed substantially in their solid state morphologies, EAA was combined with PEO as melt blends and as coextruded films with many alternating, continuous microlayers of EAA and PEO. The solid state structure and thermal behavior were characterized and the permeability to O₂ and CO₂ was measured at 23°C. When the PEO was dispersed as small domains, the particles were too numerous for most of them to contain a heterogeneity that was sufficiently active to nucleate crystallization at the normal T_c. The rubbery, amorphous nature of the PEO domains enhanced the gas permeability of the melt blends. In contrast, the constituent polymers maintained the bulk properties in 5–20 μm‐thick microlayers. The series model accurately described the gas transport properties of microlayered films. Comparison of blends and microlayers revealed that the high CO₂ selectivity of PEO was most effectively captured when the PEO phase was continuous, as in the microlayers or in the cocontinuous 50/50 (wt/wt) melt blend. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008.     

Experimental investigation and modeling of the solubility of carvedilol in supercritical carbon dioxide

This study was aimed to measure the solubility of carvedilol in the temperature and pressure ranges of 308⿿338 K and 160 bar to 400 bar, respectively. In this direction, a homemade high pressure visual equilibrium cell was used to measure the solubility of carvedilol using a static method coupled with gravimetric technique. The results revealed that the carvedilol solubility was ranged between 1.12 ÿ 10^⿿5 and 5.01 ÿ 10^⿿3 based on the mole fraction (mole of carvedilol/mole of carvedilol + mole of CO₂) in this study as the temperature and pressure was changed. Finally, the results were correlated using four density-based semi-empirical correlations including Chrastil, Mendez⿿Santiago⿿Teja (MST), Bartle et al., and Kumar and Johnston (K-J) models. Results revealed that although the K-J model leads to the lowest average absolute relative deviation percent (AARD %) of 6.27%, but it could not be considered as the most accurate correlation since all the used four correlations introduces AARD % of about 6⿿10% which may be in the same range as the experimental error.     

High‐pressure viscosity of polystyrene solutions in toluene + carbon dioxide binary mixtures

High‐pressure viscosity of polystyrene (M_w = 50,000, M_w/M_n ≤ 1.06) solutions in toluene and in mixtures of toluene + carbon dioxide was measured using a falling cylinder‐type viscometer at 320, 340, and 360 K, and up to 35 MPa. Solutions with polystyrene concentrations of 3, 5, and 7 wt % were investigated. Carbon dioxide levels in the range from 0 to 14.7 wt % were evaluated. Viscosity was observed to vary linearly with pressure at the temperatures and polymer concentrations investigated. Viscosity of the polymer solutions decreased as the concentration of carbon dioxide in the mixture was increased. The largest viscosity reduction was observed at the lowest temperature and at the highest concentration of polymer. The viscosity of the solutions was correlated with the solution density for different compositions. It was found that solutions of the same density have different viscosities, depending upon the carbon dioxide concentration in the mixture. The solutions with the higher carbon dioxide content display the lower viscosities at a given density. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 306–315, 2000     

二氧化碳水合物导热和热扩散特性

热导率和热扩散率是天然气水合物资源开采关键性基础热物性数据,采用反应釜内壁衬有氟塑料材料,低过冷度,让水合物在反应釜内逐层生成的合成方法,获得可直接用于导热测试的二氧化碳水合物样品。采用瞬变平面热源法原位测试了温度264.68～282.04 K、压力1.5～3 MPa二氧化碳水合物热导率、热扩散率,并测试了二氧化碳水合物在268.05 K、0.6 MPa左右发生自保护效应过程中热导率、热扩散率,获得了晶态下和自保护效应过程中的二氧化碳水合物热导率、热扩散率变化特性。测试结果将为天然气水合物资源的开发利用提供基础数据和理论依据。     

Oxidation of cellulose in pressurized carbon dioxide

This work presents first results upon oxidation of type II cellulose by nitrogen dioxide dissolved in carbon dioxide at high pressure. This reaction leads to oxidized cellulose, a natural-based bioresorbable fabric used for biomedical applications. The oxidation reaction takes place in a heterogeneous fluid-solid system. Kinetics of oxidation is presented here and effects of operating conditions such as pressure, temperature and initial moisture content of cellulose are investigated. Results are presented in terms of degree of oxidation of cellulose and quality of the final oxidized cellulose, which has been characterized using liquid-state and solid-state ¹³C NMR. The experimental results show the existence of possible secondary reactions which may lead to oxidized cellulose with insufficient mechanical strength. An attempt is made to evidence and understand the role of CO₂ as a solvent in this system. Indeed, although supercritical CO₂ appears to be a suitable candidate as a solvent for oxidation reactions, some inhibiting effect on nitrogen dioxide activity are observed in this case.     

Raman spectroscopic study of effect of steam and carbon dioxide activation on microstructure of polyacrylonitrile‐based activated carbon fabrics

This work presents the different effects of steam and carbon dioxide activation on the microstructure of an oxidized polyacrylonitrile (PAN) fabric. An investigation was conducted on a series of carbonized fabrics and two series of activated carbon fabrics. The fabrics were activated by steam and carbon dioxide using heat‐treatment temperatures of 900–1100°C. Steam and carbon dioxide developed the microstructure initially present in the PAN‐based activated carbon fabrics, but with different effects. These fabrics in the form of fabric and powder were examined by X‐ray diffraction and Raman spectrometry. This study indicated that carbon dioxide only reacted with the crystalline edges or the irregular carbon on the fiber surface and that the inside structure of the fibers was not greatly affected. When the fabrics were activated using steam, water molecules reacted not only on the fiber surface but also with the carbon at the crystal edge and/or the nonregular carbon in the fibers, which led to communicating pore structures on the surface and in the inner portions of the fiber. This activation also promoted the denitrogenation reactions. Because of these structures and reactions, the activated carbon fabrics, which were activated by steam, had the highest stacking height for carbon layer planes (L_c), the highest number of layer planes (L_c/d₀₀₂), the highest oxygen content, the largest crystal size (L_a), and the highest density over the other samples. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1090–1099, 2001     

Dew‐point measurements for water in compressed carbon dioxide

When transporting CO₂ for sequestration, it is important to know the water dew point in order to avoid condensation that can lead to corrosion. A flow apparatus to measure the water content at saturation in a compressed gas has been constructed. A saturator humidifies the flowing gas by equilibrating it with liquid water. Then, a gravimetric hygrometer measures the water mole fraction of the humid gas. Dew‐point data for H₂O in CO₂ on six isotherms between 10 and 80 °C at pressures from 0.5 to 5 MPa are reported. The uncertainties in water content at the dew point (expanded uncertainty with coverage factor k = 2) are on average 0.3%, significantly smaller than in any previous work. The data have been analyzed to extract the interaction second virial coefficient; the values are consistent with the theoretical estimates of Wheatley and Harvey but have a much smaller uncertainty. Published 2015 American Institute of Chemical Engineers AIChE J, 2015 © 2015 American Institute of Chemical Engineers AIChE J, 61: 2913–2925, 2015     

Influence of carbon black dispersion on the thermal diffusivity of an SBR vulcanizate

There are few investigations of the influence of filler dispersion on the thermal diffusivity of carbon black rubber compounds. In this article, experimental results of a cured styrene–butadiene rubber (SBR) compound are presented in the range of temperatures between 210 and 350 K at four levels of dispersion obtained in a laboratory mill. The results of thermal diffusivity measurements are discussed in the frame of competitive mechanisms appearing during mixing and involving the breakdown of agglomerates into aggregates and particles in the rubber matrix. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1379–1385, 1999     

Dispersion copolymerization of acrylonitrile‐vinyl acetate in supercritical carbon dioxide

Dispersion copolymerization of acrylonitrile‐vinyl acetate (AN‐VAc) had been successfully performed in supercritical carbon dioxide (ScCO₂) with 2,2‐azobisisobutyronitrile (AIBN) as a initiator and a series of lipophilic/CO₂‐philic diblock copolymers, such as poly(styrene‐r‐acrylonitrile)‐b‐poly(1,1,2,2‐tetrahydroperfluorooctyl methacrylate) (PSAN‐b‐PFOMA), as steric stabilizers. In dispersion copolymerization, poly(acrylonitrile‐r‐vinyl acetate) (PAVAc) was emulsified in ScCO₂ effectively using PSAN‐b‐PFOMA as a stabilizer. Compared with the precipitation polymerization (absence of stabilizer), the products prepared by dispersion polymerization possessed of higher yield and higher molecular weight. In addition, the particle morphology of precipitation polymerization was irregular, but the particle morphology of dispersion polymerization was uniform spherical particles. In this study, the effects of the initial concentrations of monomer and the stabilizer and the initiator, and the reaction pressure on the yield and the molecular weight and the resulting size and particle morphology of the colloidal particles were investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5640–5648, 2006     

CO2的绿色利用技术研究进展

近年来CO2的综合利用越来越引起人们的重视。本文介绍了近年来通过化学途径实现CO2资源化利用的研究方向及进展,并报道了最新的研究技术和成果。通过适当的化学反应,CO2可以转化为液体燃料、甲醇、碳酸酯类等高附加值的产品,还可通过CH4–CO2催化重整制成合成气来制备乙烯或含氧化合物等。另外,本文还介绍了其它新型CO2化学利用技术,如通过合理设计的化学肺可将CO2直接转换为氧气,利用太阳能、电能和生物微藻技术实现CO2向有用化学品的转化以及作为新型储氢材料的研究利用进展。     

超临界CO_2流体萃取植物油的实验研究

建立了一套超临界流体萃取实验装置,就大豆和花生两种植物油超临界流体萃取进行了较为详细的实验研究.在探讨了压力、温度、颗粒度、空隙率以及时间等对萃取率的影响之后,获得了指导实际生产的最佳工艺参数条件.