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Article
Prediction and Correlations of Residual Entropy of Superheated Vapor for Pure Compounds

Authors: Mahmoud O. Abdullah --- Sarmad T. Najim --- Shahad Z. Atta
Journal: Iraqi Journal of Chemical and Petroleum Engineering المجلة العراقية للهندسة الكيمياوية وهندسة النفط ISSN: 19974884/E26180707 Year: 2012 Volume: 13 Issue: 2 Pages: 11-27
Publisher: Baghdad University جامعة بغداد

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Abstract

Prediction of accurate values of residual entropy (SR) is necessary step for the calculation of the entropy. In this paper, different equations of state were tested for the available 2791 experimental data points of 20 pure superheated vapor compounds (14 pure nonpolar compounds + 6 pure polar compounds). The Average Absolute Deviation (AAD) for SR of 2791 experimental data points of the all 20 pure compounds (nonpolar and polar) when using equations of Lee-Kesler, Peng-Robinson, Virial truncated to second and to third terms, and Soave-Redlich-Kwong were 4.0591, 4.5849, 4.9686, 5.0350, and 4.3084 J/mol.K respectively. It was found from these results that the Lee-Kesler equation was the best (more accurate) one compared with the others, but this equation is sometimes not very preferable. It was noted that SRK equation was the closest one in its accuracy to that of the Lee-Kesler equation in calculating the residual entropy SR of superheated vapor, but it was developed primarily for calculating vapor-liquid equilibrium and to overcome this problem, efforts were directed toward the possibility of modifying SRK equation to increase its accuracy in predicting the residual entropy as much as possible. The modification was made by redefining the parameter α in SRK equation to be a function of reduced pressure, acentric factor, and polarity factor for polar compounds in addition to be originally function of reduced temperature and n parameter –which is also function of acentric factor– by using statistical methods. This correlation is as follows: This new modified correlation decreases the deviations in the results obtained by using SRK equation in calculating SR when comparing with the experimental data. The AAD for 2791 experimental data points of 20 pure compounds is 4.3084 J/mol.K while it becomes 2.4621 J/mol.K after modification. Thus SRK equation after this modification gives more accurate results for residual entropy of superheated vapor of pure 20 compounds than the rest of the equations mentioned above.


Article
Composition and Temperature Dependence of Excess Volume of Heavy Oil-Stocks Mixtures + (Gas oil or Toluene or Reformate)
تاثير النسب الوزنية ودرجة الحرارة على الحجم الزائد للاساسات زيت التزليقبوجود المضافات الهيدركاربونية (زيت الغاز+ التلوين + الريفورميت)

Authors: Shahad Z. Atta شهد زهير عطا --- Haidar M. Al-Qamaje حيدر موفق توفيق --- Ezzat N. Slaiman عزت نيازي سليمان
Journal: Al-Khwarizmi Engineering Journal مجلة الخوارزمي الهندسية ISSN: 18181171 23120789 Year: 2011 Volume: 7 Issue: 3 Pages: 59-67
Publisher: Baghdad University جامعة بغداد

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Abstract

Binary mixtures of three, heavy oil-stocks was subjected to density measurements at temperatures of 30, 35 and 40 °C. and precise data was acquired on the volumetric behavior of these systems. The results are reported in terms of equations for excess specific volumes of mixtures. The heavy oil-stocks used were of good varity, namely 40 stock, 60 stock, and 150 stock. The lightest one is 40 stock with API gravity 33.69 while 60 stock is a middle type and 150 stock is a heavy one, with API gravity 27.74 and 23.79 respectively. Temperatures in the range of 30-40 °C have a minor effect on excess volume of heavy oil-stock binary mixture thus, insignificant expansion or shrinkage is observed by increasing the temperature this effect becomes more significant although the heavy oil-stocks is spiked with hydrocarbons like (gas oil, toluene and reformate). Blending of Heavy oil-stocks with hydrocarbons spikes (gas oil, toluene and reformate) form non-ideal mixtures, for which excess volume can be positive or negative depending on nature species. Spiking of Heavy oil-stocks with either gas oil or reformate resulted in negative excess volume. This shrinkage is greater for the lowest boiling point spike as in the case of reformate, While, the presence of methyl groups in aromatic rings results in a positive excess volume, as shown in toluene when blended with 40 stock but a negative excess volume was found when blended with 60 stock and 150 stock. The API gravity of heavy oil-stocks has an effect on excess volume when the oil-stocks spiked with hydrocarbons like (gas oil, toluene and reformate). This 40 stocks as a typical light types resulted in minimum negative excess volume of -0.47 at 30 °C, when it was spiked with the gas oil; while the spiked heavy oil-stock with kerosene shows a maximum excess volume of -15.56 at 40 °C.

تم استخدام ثلاث انواع من اساسات زيت التزليق وهي الاستوك 40 وهو الاخف من حيث الوزن الجزيئي والمتوسط وهو الاستوك 60 والاثقل وزنا جزئيا الاستوك 150 لمعرفة السلوك الحجمي لمخاليط تلك الزويت وكذلك سلوك تلك الزيوت حجميا عند اضافة المضافات الهيدروكاربونية مثل (زيت الغاز و التلوين و الريفورميت) وكذلك بدرجات حرارة متغيرة (30-40 °م). حيث ان اضافة هذه المواد تؤدي الى زيادة في الحجم قد تكون موجبة او سالبة بمعنى اخر ان هذه الاضافات قد تودي الى انكماش او تمدد حجمي في تلك الخلائط. كما ان لدرجة الحرارة تاثير ملحوظ على الزيادة الحجمية لكل مزيج تمت دراسته. حيث تبين ان اضافة المادة الهيدروكاربونية ذات الطابع البرافييني (زيت الغاز) يؤدي الى حدوث انكماش ملحوظ في حجم الخلائط وكذلك المواد الهيدروكاربونية ذات درجة الغليان الواطى كما هو الحال في (الريفورميت) بينما اضافة المادة الهيدروكاربونية ذات الطابع الوروماتي (التلوين) يؤدي الى تمدد تلك الخلائط ماعدا خلائط الاستوك 150و 60 حيث ان اضافة التلوين الى تلك الخلائط يؤدي الى انكماشها والسبب في سلوك الزايلين بصورة عامة يرجع الى وجود مجموعتي المثيل في الحلقة (التلوين). تم الحصول على اعلى نسبة من الوزن الزائد وهي 15,56 عند اضافة الريفورميت الى الاستوك 150.

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