Theoretical Study On Critical Properties Of Binary Systems With Supercritical Carbon Dioxide

Supercritical fluid is a state that its temperature, pressure and density are higher than itscritical value. Being in-noxious, non-taste, in-inflammable, and the carbon dioxide become anoticed supercritical fluids media. In order to make a deep investigation for development and application of the supercriticalfluid technology, the investigation of thermodynamics and physical chemistry properties ofsupercritical fluid must be done. Investigators are studying the supercritical CO2 phaseequilibrium. Few reports are presented on supercritical CO2binary systems, therefor supercriticalbinary systems data is lack, and the experimental data of multi-component systems phaseequilibrium is little. It is very important to measure and study the supercritical point of CO2binarysystems. Catalyst Office of Beijing University of Chemical Technology designs a pressure resistanttank with a view cell, which was used to measure the critical point of six binary systems and theopalescence can be observed. These systems are CO2 + cyclohexane, CO2 + toluene, CO2 +n-butanal, CO2 + i-butanal, CO2 + methanol and CO2 + ethanol, in which the data of CO2+cyclohexane, CO2 + n-butanal and CO2 + i-butanal have never been found in theinterrelated reference. The experimental phenomena are observed that the critical temperaturesand critical pressures are different with various second components and the critical temperatureand critical pressure of binary system rose after the second component was added into the pureCO2. Aconclusion can be drawn out that the second component and its content affected thecriticalpropertiesofbinarysystems. In this paper, the critical temperatures and critical pressures were calculated. In calculation,the equation of mixture criticaltemperature andthe attractive part of equation of state weremodified. First, the mixing rule of temperature calculation equation was modified. The content andacentric factor of second component were introduced into the interaction parameter, and anewequationofcriticaltemperatureformixtureweresetupas: Second, the van der Waals type cubic equation of state was used to calculate the criticalpressure of the binary systems. By introducing the temperature and acentric factor into the - 4 -申 请 北 京 化 工 大 学 博 士 学 位 论 文mixingruleofattractivepartoftheequationofstate,anewexpressionwassetup. The critical temperatures and critical pressures were calculated by using modified equation.The coefficients of interaction parameter expressions were gained from the reference data; thecalculation results are agreement with the data well. It suggests that the expressions ofinteraction parameter and modification of mixing rules were corrected and the interactionparameterplayasoleofadjustment. Artificial neural network is a new type of subject with a fast development. It originated fromphysic, and permeated into various subject. In chemistry and chemical engineering, someresearcher applied the ANN into some fields. The ANN was used to research the critical propertiesof pure substances, the density and excess properties of mixtures. It is found that fewerresearcher appliedtheANNinstudyingoncriticalpointofCO2binarysystems. 1) According to the principle of the ANN structure, the ANN was applied into the studyingonthe critical properties of CO2 binary systems. Different network structures were designed by theexperiment. It suggests that ANN not only can study one type critical character that is oneoutput,butalsocanapplyforstudyingontwokindscriticalpropertiesthatistwooutput. 2) The network is 2×3×1 when the object is temperature or pressure of mixture. In order tocalculate the pressure and temperature, the structure of network was changed into 3×3×2. It canbefoundthatwhenthesystemsandobjectsaredifferent,structuresaredifferent. 3) Three different transfer function, as tansig, logsig and pureline, were disused to choice thebest combination of tra...