Molweight Molecular Weight Average Boiling Point Gravity

Reference data and engineering information about molweight molecular weight average boiling point gravity for thermodynamics applications.

molweightmolecularweightaverage

Overview

Engineering reference data for Molweight Molecular Weight Average Boiling Point Gravity in thermodynamics.

Key Formulas

First Law

$\Delta U = Q - W$

Energy is conserved — heat added minus work done.

Ideal Gas Law

$PV = nRT$

Relates pressure, volume, and temperature of an ideal gas.

Carnot Efficiency

$\eta = 1 - T_C/T_H$

Maximum efficiency between two temperatures.

Variables

Symbol	Description	Unit
$U$	Internal energy	J
$Q$	Heat	J
$W$	Work	J
$P$	Pressure	Pa
$V$	Volume	m³
$T$	Temperature	K

Key Formulas (Extended)

Riazi-Daubert 1980: $MW = 4.5673 \times 10^{-5} \cdot T_R^{2.1962} \cdot S^{-1.0164} \quad \text{(1)}$ $MW = 1.6607 \times 10^{-4} \cdot T_K^{2.1962} \cdot S^{-1.0164} \quad \text{(2)}$

Riazi-Daubert Extended: $MW = 20.486 \cdot T_R^{1.26007} \cdot S^{4.98308} \cdot e^{\left(1.165 \times 10^{-4} T_R - 7.78712 S + 1.1582 \times 10^{-3} T_R \cdot S\right)} \quad \text{(3)}$ $MW = 42.965 \cdot T_K^{1.26007} \cdot S^{4.98308} \cdot e^{\left(2.097 \times 10^{-4} T_K - 7.78712 S + 2.08476 \times 10^{-3} T_K \cdot S\right)} \quad \text{(4)}$

Applicability and Accuracy

Equations (1) and (2) are not suitable for hydrocarbons above C₂₅ (boiling point > 400°C / 750°F). For heavier oils, equations (3) and (4) are recommended.

Valid Property Ranges:

Molecular Weight (MW): 70 to 700 kg/kmol
Mean Average Boiling Point (MeABP): 20 - 560°C (90 to 1050 °F)
API Gravity: 14° to 93°
Specific Gravity (S): 0.630 to 0.973

The average prediction error for these models is approximately 7%.

Application Examples

Example 1: Molecular Weight of Naphtha

Given:

Specific Gravity (S) = 0.763
Mean Average Boiling Point (MeABP) = 292°F

Step 1: Convert temperature to Rankine (°R) MeABP = 292°F + 460 = 752°R

Step 2: Calculate using Eq. (1) MW = 4.5673E-05 * 752^2.1962 * 0.763^-1.0164 = 124.6 kg/kmol

Step 3: Verify using Eq. (3) MW = 20.486 * 752^1.26007 * 0.763^4.98308 * e^(1.165E-04752 - 7.787120.763 + 1.1582E-037520.763) = 124.8 kg/kmol

Result: The difference between the models is 0.2%.

Example 2: Molecular Weight of Light Gas Oil

Given Distillation Data (D86):

10 vol% recovered at 255°C
30 vol% recovered at 280°C
50 vol% recovered at 303°C
70 vol% recovered at 325°C
90 vol% recovered at 351°C
API Gravity = 31.4°

Step 1: Convert API to Specific Gravity S = 141.5 / (31.4 + 131.5) = 0.869

Step 2: Calculate Volume Average Boiling Point (VABP) and Slope VABP = 0.2(255+280+303+325+351) = 303 °C Slope = (351-255)/80 = 1.2 °C/% recovered

Step 3: Estimate MeABP from VABP MeABP = VABP - 5°C = 303 - 5 = 298°C MeABP in K = 298 + 273 = 571 K

Step 4: Calculate using Eq. (2) MW = 1.6607E-04 * 571^2.1962 * 0.869^-1.0164 = 217 kg/kmol

Step 5: Verify using Eq. (4) MW = 42.965 * 571^1.26007 * 0.869^4.98308 * e^(2.097E-04571 - 7.787120.869 + 2.08476E-035710.869) = 232 kg/kmol

Result: The difference between the models is 6.5%.

References

Original Source

Source: engineeringtoolbox.com