共查询到19条相似文献,搜索用时 187 毫秒
1.
2.
3.
热力学模型预测低温下柴油中正构烷烃的析出 总被引:1,自引:0,他引:1
根据柴油的组成复杂的特点,采用状态方程描述液相,溶液理论描述固相,对低温下柴油液固两相平衡的液相组成和固相组成进行了计算。并将正构烷烃以外的其它组分作为一个虚拟组分,简化了组分极其复杂的柴油。应用建立的模型计算了两种柴油的析蜡温度,并与柴油的实测浊点进行了比较,结果表明选择的热力学模型适用于低温下柴油液固两相平衡的计算。根据计算得到的液相组成和固相组成,分析了低温下柴油中各正构烷烃析出的趋势,结果表明碳数越大的正构烷烃虽析出趋势大,但由于在整个正构烷烃中所占比例较小,故其在固相中的比例依然较小;碳数为20左右的偶数正构烷烃,最容易析出。随着温度的降低,析出固体中正构烷烃的平均碳数变小。并根据计算结果较好地解释了低温时析出固相中始终存在非正构烷烃组分的实验现象。 相似文献
4.
非电解质固液平衡模型对石油化工流程模拟的结晶过程计算具有重要作用。采用2种不同体系的实验数据,从基于正规溶液理论和局部组成理论的6种非电解质固液相平衡模型出发,依次评价了它们对固相分率和固相组成的计算精度,并对相平衡计算模型进行改进。6种相平衡模型对固相分率计算结果的平均绝对偏差(AAD)介于2.58%~9.14%。研究发现,预测模型中的固液相焓差修正项影响固液相平衡预测结果的准确性。通过在Won、P-UNIQUAC和P-UNIQUAC(Ghanaei)相平衡模型中分别增加Pedersen、Ghanaei和DIPPR固液相焓差修正项改进模型并用实验数据进行评价。结果表明,9种改进的相平衡模型对固相分率的计算结果优于原始模型,对固相分率计算结果的AAD介于3.36%~6.31%。 相似文献
5.
6.
7.
液液相平衡数据是萃取分离设备设计的基础,在没有现成的相平衡数据可用时,利用较为合理的热力学模型,并充分考虑算法中应注意的一些细节问题,通过计算机编程计算就可获得各相的组成,本文对此作了较为详细的阐述。 相似文献
8.
针对对二甲苯装置结晶单元中由苯和二甲苯组成的相关体系,选取了固液相平衡计算模型—Van′t Hoff方程简式,利用与苯和二甲苯有关的二元和三元体系固液相平衡文献数据对该模型进行考察,利用该模型预测由苯和二甲苯组成的二元和三元体系的固液相平衡数据,并绘制三元体系的固液相平衡相图。结果表明:采用Van′t Hoff方程简式计算,苯和二甲苯有关体系的液相摩尔分数的平均相对偏差为2.69%,低共熔点温度的偏差最高为0.59℃,最低为0.01℃,表明所选模型适用于由苯和二甲苯组成的体系固液相平衡计算;利用该模型预测苯-间二甲苯、苯-邻二甲苯二元体系及对二甲苯-间二甲苯-苯、对二甲苯-邻二甲苯-苯、间二甲苯-邻二甲苯-苯三元体系的固液相平衡数据,绘制了对二甲苯-间二甲苯-苯三元体系的固液相平衡相图,这些新的相平衡数据和相图均未见有文献报道,可为对二甲苯结晶相关体系的固液相平衡研究提供理论指导和依据。 相似文献
9.
《高校化学工程学报》2015,(6)
液液相平衡数据是化工萃取过程设计和模拟计算的基础,为了给以甲基戊烯酮为溶剂的含酚废水萃取过程设计和流程模拟计算提供基础数据,本实验采用平衡法分别测定了25、40和50℃常压下甲基戊烯酮-水-苯酚三元物系液液相平衡数据,并绘出了各温度下的分配系数曲线。同时,采用NRTL活度系数模型对实验数据进行了关联,回归得到了该三元物系的二元交互参数。运用回归得到的模型参数,对该三元物系的相平衡数据进行计算,结果表明该模型可以很好地关联实验数据,模型计算值与实验值的相对均方根误差和绝对平均误差均在1.5%以内。 相似文献
10.
11.
对二甲苯结晶过程的固液相平衡研究 总被引:1,自引:0,他引:1
使用Van’t Hoff方程、Hildebrand方程和冰点降低常数法计算了PX-MX二元体系的固液平衡相图,计算结果表明,3种计算方法均与实验结果吻合很好。使用冰点降低常数法计算混合二甲苯多元体系的低共熔点组成,计算结果表明,含有EB的多元体系,其液相不能当作是理想溶液,不含EB的多元体系,其液相可以近似当作是理想溶液,在工业生产分析时,PX-MX-OX-EB可以近似为PX-MX-OX三元体系。根据冰点降低常数法的计算结果,绘制了PX-MX-OX三元体系的固液平衡立体相图,并分析了不同工业原料中对二甲苯的结晶过程,计算结果表明,PX结晶过程的回收率都受到低共熔点的限制,对于PX质量分数为21.5%的低含量进料,PX最大回收率为67%,对于PX质量分数为83.72%的高含量进料,PX最大回收率为97%。 相似文献
12.
This study is aimed at developing a simple and stable method for accurately calculating the three-phase compositions existing at equilibrium in VLLE region. Incorporation of a simple method for estimating initial K-values in the present algorithm allows this algorithm to more easily and accurately calculate the composition of each phase in vapor–liquid–liquid equilibrium. The old algorithms have not used the above method but used trial and error procedures (such as minimization of Gibbs free energy) which is more difficult and time consuming. Compared with the experimental data, the present method gives more reasonable results. 相似文献
13.
采用等温溶解平衡法研究了288、298、308 K下三元体系KCl-PEG4000-H2O的相平衡关系,绘制了相应的相图、密度-组成图和折射率-组成图。研究发现:288、298、308 K下,三元体系KCl-PEG4000-H2O无分层现象,只存在固液相平衡关系,其平衡相图由不饱和液相区(L)、一固一液区(S+L)和两固一液区(2S+L)构成,且两固一液区随温度升高减小。KCl溶解度随着溶液中PEG4000含量不断增加而减小。溶液中PEG4000含量小于0.50时,盐析率受温度影响较小;含量大于0.50时,盐析率随着温度升高呈减小趋势。采用修正后的Pitzer方程进行了三元体系KCl-PEG4000-H2O (288、298、308 K)溶解度计算,对比发现,理论计算值与实验值吻合较好。 相似文献
14.
采用等温溶解平衡法和浊点法分别测定了308.2 K时三元体系KCl+PEG10000/20000+H2O的固液平衡组成和液液平衡组成,同时测定了固液平衡时体系的密度和折射率。根据实验数据,绘制了两个三元体系308.2 K时的完整相图、双液线对比图和结线-组成图。研究发现:三元体系KCl+PEG10000/20000+H2O 308.2 K时的完整相图均包含6个区域:不饱和液相区(L),2个一固一液区(L+S),双液相区(2L),两液一固区(2L+S),两固一液区(L+2S);其中,一液两固区(L+2S)中的两种固相分别为KCl和PEG10000/20000。在完整相图中,一固一液区面积最大,双液相区面积最小。对比308.2 K时聚乙二醇分子量为1000、4000、6000、10000和20000的KCl+PEG+H2O体系可知:分子量为1000、4000和6000时,体系中仅存在固液相平衡关系;分子量为10000和20000时,体系中同时存在固液和液液相平衡关系,且随着聚乙二醇分子量的增加,双液线向原点移动,双液相区(2L)和两液一固区(2L+S)增大,不饱和液相区(L)和一固一液区(L+S)均减小。采用Chen-NRTL-PDH热力学模型进行了液液相平衡计算,计算结果与实验数据吻合较好。 相似文献
15.
16.
Yiping Tang Grant Stephenson Ensheng Zhao Mayur Agrawal Sanjoy Saha 《American Institute of Chemical Engineers》2012,58(2):591-599
The equal‐area (EA) method is studied with respect to its applicability to a wide range of phase equilibrium scenarios for pure fluids and binary mixtures. The study covers vapor‐liquid equilibrium (VLE), liquid–liquid equilibrium (LLE), solid‐liquid equilibrium (SLE) and their crossover transitions. The thermodynamic models studied include equation of state, activity coefficient and solid solubility models and their combinations. The performance of the EA method for chain molecules, at very low temperature and nearby the critical point is also investigated. We conclude that the EA method is very reliable and efficient and has a number of advantages over the conventional method. Finally, we apply the EA method to the regression of the model parameters to demonstrate its attractive application. © 2011 American Institute of Chemical Engineers AIChE J, 2012 相似文献
17.
Considering the limitations of experimental studies on thermophysical properties of cryogenic phase change materials (PCMs), a highly accurate approach to predict the solid-liquid equilibrium (SLE) of PCMs is proposed, in which the method of referenced state by a hypothetic path is used in the fugacity of PCMs in the solid phase and the Soave-Redlich-Kwong (SRK)-UNIFAC model is applied in the liquid phase. Based on this method, the thermophysical properties of cryogenic composite PCMs including eutectic composition, eutectic temperature, and eutectic enthalpy are predicted with a minor deviation. Taking the liquid natural gas (LNG) air separation unit as an example, the established simulating method with high accuracy to predict the thermophysical properties of the PCMs is adopted for material selection and design for a cold storage unit in this project with high efficiency. 相似文献
18.
A new algorithm has been developed for solving the multicomponent vapor-liquid-liquid equilibrium Mash problem. The algorithm is an extension of the “inside-out” approach proposed by Boston and Britt for the vapor-liquid equilibrium flash problem. Conventional flash algorithms use temperature, pressure, composition, and phase fraction as the problem independent variables, In the inside-out approach a new set of independent variables is introduced in place of the conventional variables. The new variables are chosen to be as independent as possible of the conventional variables and as free as possible of mutual interaction. Complex phase equilibrium models are used only to generate parameters for a simple equilibrium ratio model. These parameters become the problem independent variables. The Quasi-Newton method of Broyden is employed to promote convergence of these variables. The algorithm first obtains a solution for the vapor-liquid equilibrium flash. By examining the liquid phase, a heuristic algorithm is employed which quickly locates a two liquid phase composition region of reduced total system free energy when the original liquid is unstable. The solution of the vapor-liquid-liquid equilibrium flash is initiated only when this occurs. The performance of the algorithm is demonstrated by a number of problems which exhibit varying degrees of nonideality. 相似文献
19.
Solokhin M. A. Solokhin A. V. Timofeev V. S. 《Theoretical Foundations of Chemical Engineering》2002,36(6):564-569
A new method is suggested for calculating liquid–liquid equilibrium. The method requires the global structure of the phase diagram to be determined. An algorithm for the automated synthesis of diagram structures is developed. 相似文献