Physical properties of HC systems

PHYSICAL PROPERTIES OF HYDROCARBON SYSTEMS e A reliable estimate of physical properties is required in order to obtain reliable calculations For single component systems data are readily available Tables 3.1 and 3.2 are examples of such data that will be used for calculations References 3.1-3.3 may be used to estimate properties of pure paraffins heavier than decane Note: Table 3.2 is in two parts Table 3.2(a) is in SI units and Table 3.2(b) is in FPS units This is the system used throughout this book when corresponding tables and figures are shown in separate units TABLE 3.1 =.- Compound Molecular Weight Physical Constants Critical Pressure r - MPa Acentric Factor o - c1 16.043 666 4.60 0.0104 c2 30.070 707 4.88 0.0979 c3 44.097 617 4.25 0.1522 iC4 58.124 528 3.65 0.1852 nC4 58.124 551 3.80 0.1995 iCs 72.151 491 3.39 0.2280 nC5 72.151 489 3.37 0.2514 nC6 86.178 437 3.01 0.2994 nc7 100.205 397 2.74 0.3494 ncs 114.232 361 2.49 0.3977 nC9 128.259 332 2.29 0.4445 nC1o 142.286 305 2.10 0.4898 ncll 156.302 285 1.97 170.338 1.82 d nC12 - 0.5350 0.5620 - - N2 28.016 493 3.40 0.0372 co2 44.010 1071 7.38 0.2667 H2S 34.076 1300 8.96 0.0948 02 32.000 731 5.04 0.0216 H2 2.016 188 - CHAPTER psia - - 8.015- 3199 1.30 22.06- - -0.2202 - - - 0.3443 45 PHYSICAL PROPERTIES OF HYDROCARBON SYSTEMS Nonideal P-V-T Equations A large number of P-V-T equations have been developed to describe nonideal, real gas behavior Each is empirical in that it correlates a specific set of data using one, or more, empirical constants There can be as many such equations as there are people who correlate data Some of the most common equations are summarized below The inclusion, or exclusion, of an equation is not a reflection of the worth of an equation It merely reflects degree of recognition in this industry van der Waals Where: a &b v = = correlation constants 'molar volume Benedict-Webb-Rubin (BWR) Where: P T = = = y = absolute pressure absolute temperature molar density correlation constants Redlich-Kwong (RK) Where: a &b = v = correlation constants molar volume Peng-Robinson (PR) RT -a(T) v - b v(v+b)+b(v-b) d The van der Waals equation is the "grandfather" of P-V-T equations It is seldom used today but serves as a basis for many concepts used in the correlation of mixture properties Equations 3.2, 3.4 and 3.5 are called cubic equations of state because they are cubic when writ,ten in terms of volume The constants a and b are a hnction of the critical properties T, and PCand a third parameter, usually the acentric factor, a For mixtures, mixing rules are necessary to determine the values of a and b Mixing rules will be discussed briefly in a later section A number of nlodifications to these equations of state have been published and are used in the oil and gas industry The purpose of the nlodifications is to improve the validity of the model Examples include the Soave modification to the RK equation (SRK) and the Starling modification to the BWR equation (BWRS) The above equations are used primarily as a basis for computer solutions They tend to offer more precision, but the real accuracy of the results may be no better than the simpler methods when one considers the quality o f the P: T, and composition data available for use in predicting behavior of actual systems - 52 - - - - - p p - - - - - VOLUME 1: THE BASIC PRINCIPLES ... PHYSICAL PROPERTIES OF HYDROCARBON SYSTEMS Nonideal P-V-T Equations A large number of P-V-T equations have been developed to describe nonideal,... equations are summarized below The inclusion, or exclusion, of an equation is not a reflection of the worth of an equation It merely reflects degree of recognition in this industry van der Waals Where:... "grandfather" of P-V-T equations It is seldom used today but serves as a basis for many concepts used in the correlation of mixture properties Equations 3.2, 3.4 and 3.5 are called cubic equations of state