苯-烯烃-N-甲基吡咯烷酮汽液平衡的研究

N-甲基吡咯烷酮(NMP)作为优良的萃取剂,广泛地被用于芳烃的抽提中,但其与苯及C6～C8烯烃之间的汽液平衡基础数据却极为贫乏.采用CE-2型汽液平衡数据测定仪,测定了常压下苯-1-己烯-NMP、苯-1-庚烯-NMP、苯-1-辛烯-NMP三组三元汽液平衡数据;对三组三元体系,分别以实测数据用Wilson、NRTL和UNIQUAC模型进行了关联,所得三元体系汽相组成计算值和实测值的平均偏差均较小(分别小于0.00839,0.00926和0.00802).研究结果补充了苯-烯烃-N-甲基吡咯烷酮的三元汽液平衡数据,为实际工程应用提供了基础数据.     

N-甲酰吗啉与苯的二元等压汽液平衡

石化系统、焦化行业,采用N-甲酰吗啉（NFM）溶剂精制芳烃受到极大重视,但可资利用的基础数据却极为贫乏,尚无等压汽液平衡数据。用改进的EC-2型汽液平衡釜,测定了常压下苯-NFM、甲苯-NFM二元体系汽液平衡数据,并用 NRTL 和 UNIQUAC 模型对实验数据进行了关联,得到了模型相应的二元交互参数。经Herington 面积法检验,上述数据满足热力学一致性要求,结果较为满意。研究结果填补了该项数据空白,完全能满足N-甲酰吗啉溶剂精制芳烃工程设计的需要。     

乙酸乙酯-苯-甲苯,四氯化碳-乙酸乙酯-苯两组三元体系汽液平衡数据的测定和关联

本文用改进的Colburn汽液平衡釜测定了在760mm汞柱压力下,乙酸乙酯-苯-甲苯和四氯化碳-乙酸乙酯-苯两组三元体系的汽液平衡数据.乙酸乙酯-苯-甲苯三元体系的分析方法采用折光指数(n_D~(20))和正常沸点两种三元物性数据相结合的物理化学分析法,四氯化碳-乙酸乙酯-苯三元体系的组成采用折光指数(n_D~(20))和密度(d_4~(25)两种物性数据相结合的方法.将所测定的两组平衡数据与纯组分的参数有关的关联式计算所得结果进行对比,获得了满意的结果.     

沸点分析法在二元和三元体系汽液平衡测定中的应用

本文用沸点分析法测定了101.325kPa压力下,苯-甲苯二元体系和苯-甲苯-四氯化碳三元体系的汽液平衡数据。为了获得该三元体系的推算结果,同时又测定了苯-四氯化碳和甲苯-四氯化碳两组二元体系的汽液平衡数据,所有二元体系的汽液平衡数据用NRTL方程进行了热力学关联,并用获得的二元参数对三元体系的汽液平衡进行了预测,预测结果和实验结果符合良好。     

苯与甲苯及C8芳烃体系固液相平衡计算

针对对二甲苯结晶体系中由苯与甲苯及C₈芳烃组成的二元、三元及多元体系,选取了固液相平衡计算模型—Van′t Hoff方程简式,利用该模型计算二元、三元及多元体系的低共熔点温度及对应的低共熔点组成,并绘制三元体系固液相平衡相图。结果表明：由Van′t Hoff方程简式得到的苯-对二甲苯二元体系固液相平衡计算结果与文献数据吻合较好,表明所选固液相平衡计算模型适合于由苯与甲苯及C₈芳烃组成的体系固液相平衡计算;利用Van′t Hoff方程简式计算得到了由苯与甲苯及C₈芳烃组成的二元、三元、四元、五元和六元体系的低共熔点温度及组成,并预测了苯-甲苯和苯-乙苯二元体系的液相摩尔分数,利用这些数据绘制了对二甲苯-甲苯-苯、对二甲苯-乙苯-苯、苯-乙苯-甲苯3个三元体系的固液相平衡相图,这些数据和相图未见文献报道,可为PX结晶相关的苯与甲苯及C₈芳烃组成的体系固液相平衡研究提供理论指导和依据。     

烷烃-芳烃-N-甲酰吗啉体系液液平衡

用液液平衡釜测定了等温下正庚烷苯ＮＦＭ、甲基环己烷苯ＮＦＭ、正庚烷甲苯ＮＦＭ和甲基环己烷甲苯ＮＦＭ等４组三元体系的液液平衡数据,用ＮＲＴＬ和ＵＮＩＱＵＡＣ模型进行了关联,求得各三元体系的褶点数据,并对ＮＦＭ溶剂存在下烷烃和芳烃的选择性进行了比较。     

乙醇-苯-氯化钙体系汽液平衡

测定了兰州大气压下溶有不同浓度氯化钙的乙醇-苯体系的汽液平衡数据,以Furter拟二元体系模型处理溶盐三元体系,用Van Laar方程对数据进行了关联,得到较好的结果。     

苯丙烯-苯乙酮-苯异丙醇汽液平衡测定与关联

采用单级循环汽液平衡装置测定常压下苯丙烯-苯乙酮-苯异丙醇(CA)体系中苯丙烯-苯乙酮、苯乙酮-苯异丙醇、苯丙烯-苯异丙醇二元及苯丙烯-苯乙酮-苯异丙醇三元体系的汽液平衡数据,分别以NRTL和UNIQUAC为相平衡模型对实验数据进行关联,从而确定相平衡模型及组分间的交互参数,并采用Herington面积法对二元汽液平衡数据进行热力学一致性检验。由关联得到的3对二元体系模型参数计算三元体系的汽液平衡数据,并与实验值进行比较。结果表明:计算值与实验值的相对误差均小于5%,说明实验值和计算值一致,且其中NRTL模型的误差更小。该结果为苯丙烯-苯乙酮-苯基异丙醇混合物的分离提供了一定的基础数据。     

四氯化碳-乙酸乙酯-苯三元体系汽液平衡规律性的研究

用改进的Colburn汽液平衡釜测定了在760毫米汞柱压力下四氯化碳-乙酸乙酯-苯三元体系的汽液平衡数据。三元体系的组成分析系采用折光指数(n_D~(20))和密度(d_4~(25))两种物性数据相结合的方法。将所测得的本三元体系的汽液平衡数据与第一报中仅与纯组分有关的参数所获得的关联式的预测值(推算值)进行对比,72组实测数据的对比结果证明了预测结果是可靠的。     

四氢萘-正癸烷-二甲基亚砜液-液平衡数据的测定与关联

煤直接液化中油中含有50%~70%的芳烃,其中80%左右为重芳烃,利用二甲基亚砜(DMSO)对液化油中芳烃萃取分离是对煤液化油进行改质的有效途径。相应体系液液平衡的测定是煤直接液化中油芳烃萃取过程研究开发的理论基础。研究测定了常压下四氢萘-正癸烷-DMSO三元体系在303.15、313.15、323.15 K时的液-液平衡数据,得到了该体系三元相图,并用Othmer-Tobias方程与NRTL方程进行了关联。体系中四氢萘对正癸烷选择性系数为3.2~17.7,表明用DMSO萃取分离四氢萘和正癸烷具有很好的性能。通过体系液-液平衡数据关联获得了NRTL方程模型参数,利用NRTL模型对该体系进行计算,计算值与实验值的平均偏差较小,说明NRTL模型适用于该体系的液-液平衡。     

Interactions between shrinkage reducing admixtures (SRA) and cement paste's pore solution

Shrinkage reducing admixtures (SRA) have been developed to combat shrinkage cracking in concrete elements. While SRA has been shown to have significant benefits in reducing the magnitude of drying and autogenous shrinkage, it has been reported that SRA may cause a negative side effect as it reduces the rate of cement hydration and strength development in concrete. To examine the influence of SRA on cement hydration, this study explores the interactions between SRA and cement paste's pore solution. It is described that SRA is mainly composed of amphiphilic (i.e., surfactant) molecules that when added to an aqueous solution, accumulate at the solution-air interface and can significantly reduce the interfacial tension. However, these surfactants can also self-aggregate in the bulk solution (i.e., micellation) and this may limit the surface tension reduction capacity of SRA. In synthetic pore solutions, SRA is observed to form an oil-water-surfactant emulsion that may or may not be stable. Specifically, at concentrations above a critical threshold, the mixture of SRA and pore fluid is unstable and can separate into two distinct phases (an SRA-rich phase and an SRA-dilute phase). Further, chemical analysis of extracted pore solutions shows that addition of SRA to the mixing water depresses the dissolution of alkalis in the pore fluid. This results in a pore fluid with lower alkalinity which causes a reduction in the rate of cement hydration. This may explain why concrete containing SRA shows a delayed setting and a slower strength development.     

Influence of bleed water reabsorption on cement paste autogenous deformation

The effects of bleed water reabsorption and subsequent early age expansion on observed autogenous deformation are investigated in this research. Bleeding was induced by varying superplasticizer and shrinkage-reducing admixture dosages and by increasing the water-to-cement ratio. This research revealed that significant early age expansion occurs with increasing chemical admixture dosages and higher water-to-cement ratios, as expected, due to increasing bleeding of those samples. When samples were rotated, negligible early age expansion was observed. Thus, bleed water reabsorption is shown to be the primary mechanism causing initial expansion in sealed autogenous deformation samples. Thermal dilation and ettringite growth appear to have a minimal influence on the observed expansion. Rotating the samples during setting eliminates the potential for bleed water reabsorption and is recommended for all autogenous deformation testing.     

Chemical model for cement-based materials: Thermodynamic data assessment for phases other than C-S-H

In the context of waste confinement, concrete may be used both as a confinement and as a building material. Concerning radwaste, the heat released during radioactive decay will modify the equilibrium constants of the minerals forming the concrete. The present work aims to elucidate the temperature dependency of the thermodynamic functions related to minerals from the concrete or associated with some of its degradation products. A large set of experimental data has been collected, for the chemical systems SO₃-Al₂O₃-CaO-CO₂-Cl-H₂O and SiO₂-Al₂O₃-CaO-H₂O, including iron and magnesium bearing phases. Most of the data collected concern experiments in aqueous media but results from calorimetric studies were also included, when available. Based on selected thermodynamic properties for each phase, predominance diagrams were drawn for the chemical elements listed above. Phase relations reported into predominance diagram appear rather consistent with most of the literature results. The case of katoite has been especially discussed, because it shows inconsistencies with respect to a hydrogarnet-grossular solid solution and with respect to phase relations reported into already published works. Finally, we underline the chemical compatibility of Portland cement pastes with carbonate aggregates, compared to silicates, for long-term storage applications.     

An investigation of microstructure evolution in cement paste through setting using ultrasonic and rheological measurements

The response of hydrating cement paste through setting are monitored using rheological measurements and ultrasonic reflection measurements. Increases in the elastic modulus and yield stress of cement paste with time are obtained from the rheological measurements. Ultrasonic measurements are performed using horizontally polarized shear waves (SH) reflected off of the hydrating cement paste. Changes in the ultrasonic signal through setting are related with changes in the porosity and stiffness of an equivalent water-filled poroelastic material, which provides identical acoustic impedance. The measured changes in the shear modulus obtained from ultrasonic measurement are shown to correlate well with increase in elastic modulus obtained from rheological measurements. The increase in the shear modulus of the porous material obtained from the ultrasonic measurements is shown to correspond well with the observed increase in the yield stress of the cement paste. By combining the information from rheological and ultrasonic measurements, it is found that even in the fluid stage there is sufficient structural integrity in the arrangement of cement grains to support low-amplitude shear stress and the evolution of a continuously connected network of cement particles within the paste is coincident with a rapid increase in the shear modulus of the porous skeleton.     

Nonlinear ultrasonic evaluation of load effects on discontinuities in concrete

The presence of discontinuity surfaces in concrete structures, i.e. two or more layers in contact, may be an existing situation with evident relapses on damage formation and progression. Differences occur depending on the type of discontinuity, which could be a thin weaker layer or a pre-existing crack. The behavior of pre-existing interfaces is here studied by means of the Scaling Subtraction Method, a Nonlinear Ultrasonic Non-Destructive Technique, that revealed to be effective in describing the mechanical evolution of concrete samples with discontinuity surfaces under the effects of compressive loads.     

Assessment of the long-term stability of cementitious barriers of radioactive waste repositories by using digital-image-based microstructure generation and reactive transport modelling

Cement-based grout plays a significant role in the design and performance of nuclear waste repositories: used correctly, it can enhance their safety. However, the high water-to-binder ratios, which are required to meet the desired workability and injection ability at early age, lead to high porosity that may affect the durability of this material and undermine its long-term geochemical performance.In this paper, a new methodology is presented in order to help the process of mix design which best meets the compromise between these two conflicting requirements. It involves the combined use of the computer programs CEMHYD3D for the generation of digital-image-based microstructures and CrunchFlow, for the reactive transport calculations affecting the materials so simulated. This approach is exemplified with two grout types, namely, the so-called Standard mix 5/5, used in the upper parts of the structure, and the “low-pH” P308B, to be injected at higher depths.The results of the digital reconstruction of the mineralogical composition of the hardened paste are entirely logical, as the microstructures display high degrees of hydration, large porosities and low or nil contents of aluminium compounds.Diffusion of solutes in the pore solution was considered to be the dominant transport process. A single scenario was studied for both mix designs and their performances were compared. The reactive transport model adequately reproduces the process of decalcification of the C-S-H and the precipitation of calcite, which is corroborated by empirical observations. It was found that the evolution of the deterioration process is sensitive to the chemical composition of groundwater, its effects being more severe when grout is set under continuous exposure to poorly mineralized groundwater. Results obtained appear to indicate that a correct conceptualization of the problem was accomplished and support the assumption that, in absence of more reliable empirical data, it might constitute a useful tool to estimate the durability of cement-based structures.     

Wavelet-based analysis of ultrasonic longitudinal and transverse pulses in cement-based materials

Ultrasonic pulse velocity has been used for decades to detect localized damage and to estimate concrete properties. More recent applications aim at diffuse damage characterization, such as environmental and mechanical damage. In most applications the methodology to calculate pulse speed is a very important issue. This work, applying continuous wavelet transform (CWT) to construct time-frequency signal representations, calculates frequency-dependent velocity of longitudinal and transverse ultrasonic pulses using wavelet scales. The method is applied to a total of 14 specimens of 5 different mixes and frequency-dependent velocities are calculated using four wavelet families. The CWT capability to decompose the inquiring pulse spectrum and analyze phase velocities is discussed with regard to wavelet, pulse type, and mixture. Frequency-dependent velocity of longitudinal pulses at lower frequencies (from 100 kHz up to 250 kHz) was proven to be much more sensitive to mix proportions than transverse pulses.     

Effects of adhesive type and polystyrene concentration on the shear strength of bonded polystyrene/high-density polyethylene blends

The lap-shear strengths of adhesively bonded polystyrene (PS), high-density polyethylene (HDPE), and their blends, were studied as a function of adhesive type and blend composition. The performance of virgin and recycled polymer systems was examined. The lap-shear strength depended strongly on the amount of PS in the blend and the type of adhesive, and the acrylic adhesives demonstrated the best performance for all compositions. Bonded strengths of HDPE increased by approximately 50% when HDPE was blended with 34% PS, the co-continuous composition. The results indicate that structural elements made from PS/HDPE immiscible blends may be effectively bonded with adhesives without expensive surface treatments.