Page 100 - Fluid Catalytic Cracking Handbook

FCC Feed Characterization 77

the refractive index at this temperature. To use the n-d-M method,
refractive index at 20°C needs to be estimated using published cor-
relations. For this reason the n-d-M method is usually employed in
conjunction with other correlations such as TOTAL. Example 2-3 can
be used to illustrate the use of the n-d-M correlations.

Example 2-3

Using the feed property data in Example 2-1, determine MW, C A, C N
and C p using the n-d-M method.

Step 1: Molecular weight determination by ASTM method.
1. Obtain viscosity at 100°F (37.8°C)
a. Plot viscosities at 130°F (54.4°C) and 210°F (98.89°C).
b. Extrapolate to 100°F, VIS = 279 SSU.
2. Convert viscosities from SUS to centistoke (csT):
a. From Appendix 6, viscosity @ 100°F = 60.0 cSt.
b. Viscosity @ 210°F = 7.37 cSt.
3. Obtain molecular weight:
a. From Appendix 5, H = 372 and MW = 430.

Step 2: Calculate refractive index @ 20°C from the TOTAL correlation.

1 2056
RI (20) = 1 + 0.8447 x (SO) ' x (VABP (deg C) + 273.16r°' 0557
0 0044
x (MW)- '

RI (20) = 1 + 0.8447 x (0.913) ' ! 2056 x 728.2^' 0557 x 446^ 0044

RI, 20) = 1.5046

Step 3: Calculate n-d-M Factors.

V = 2.51 x (RI (20) - 1.4750) - (D 20 - 0.8510) = 0.0271

V = 2.51 x (1.5046 - 1.4750) - (0.90 - 0.8510) = +0.0271

w = (D 20 - 0.8510) - 1.11 (RI (20J - 1.4750) = +0.0226

w - (0.90 - 0.8510) - 1.11 x (1.5046 - 1.4750) = +0.0226