Pereira.qxp 1/7/09 3:08 pm Page 43
A Faster Set-up for the Estimation of Microcarbon Residue for Heavy Oil and Fractions
Table 1: Carbon Residue Contents Reported/Determined* for Figure 1: Details of the Microcarbon Residue Tester
Selected Samples
A
Nature of Material Sample MCR (wt%)
N
Whole bitumen Athabasca bitumens 12.5
2
inlet Rotameter
12.6±0.6*
11.7±0.4*
Cold Lake bitumen 12.5
11.7±0.3*
Hamaca (Venezuelan heavy oil) 14.2
14.4±0.6*
Furnace MCR assembly
Vacuum residue Athabasca 15% 525°C- 25.4
23% 525°C- 17.6±0.4*
*This work; for other values see Hassan et al., Fuel, 2008;87:3631.
equipped with programmable temperature controller, as shown in Figure
1A. The apparatus (see Figure 1B) was constructed of aluminium and
B
stainless steel in order to make it light and robust. The platform on which
sample holders are placed is 4 inches in diameter. A known mass
(10–40mg) of sample was placed in a 2cc glass sample holder. The sample
holders were then placed on the platform adjacent to the purge tubings.
Twenty-six purge tubings, each
3
⁄4-inch long and
1
⁄8-inch wide, extend out
from the platform for N
2
purge close to the samples (see Figure 1C). A
glass cover 4 inches wide and 2 inches high with one
1
⁄8-inch orifice is then
placed to shield the samples from the air. The system was purged with N
2
at a flow rate of 900cc/min for 45 minutes before heating. The 2ft-long
SS tubing carrying the gas within the furnace before reaching the sample
holder acted as a pre-heater. This high flow rate of gas does not
C
significantly lower the temperature of the samples with respect to the set
point. This was checked by using an external thermocouple placed above
the sample vials during heating carried out both with and without carrier
gas. The system was designed to ensure equal N
2
flow from all 26 tubes.
Microcarbon Residue Testing Procedure
The samples in the muffle furnace were then heated to 500°C at a rate of
10°C/min. The temperature was maintained at 500 C for 20 minutes.
After heating, the samples were allowed to cool under N
2
until the
temperature dropped to 100°C. The samples were then placed in a
desiccator before measuring their final mass at ambient temperature. An
analytical balance from Mettler with ±0.01mg sensitivity was used to
weight the samples before and after heating. Figure 2 shows the results
Figure 2: Microcarbon Residue Values for Reference Standards
obtained for MCR standards using the apparatus capable of analysing 26 Determined with the 26-sample Set-up
samples at a time. The experiment was repeated at least five times to
30
ensure reproducibility of the measurements. The position of the samples y=0.991x
on the platform was also changed in order to confirm that the values
R
2
=0.9999
obtained were independent of the position of the sample. It was found
20
that for samples with varying MCR concentrations (0.35–24.5wt%), the
results obtained with the new set-up were very reproducible. A linear
regression for the data presented in Figure 2 gave a slope of 0.991
10
alues (determined) (wt%)
(R
2
=0.9999). The standard deviations for MCR values obtained were
MCR v
within the experimental error margin provided by the manufacturer. The
0
deviations for the 0.35 and 2.0wt% samples were beyond the limits 102030
accepted by the American Society for Testing and Materials (ASTM). Since MCR values (standard) (wt%)
these two samples are not representative of real heavy oil samples for
which MCR determination is meaningful, these deviations are irrelevant to determined in our laboratory. It is evident that the values determined
our work. As in any analytical method, expectable relative errors are larger in our laboratory set-up are in good agreement with those reported in
when determinations are performed within the lower end of the range. the literature. The samples were analysed at least five times to
determine the average value. It is worth pointing out that the two
Application to Real Heavy Oil Samples Athabasca residua samples, which contained different residual
Table 1 lists the carbon residue contents reported for selected bitumen fractions, provided different MCR contents. As expected, the sample
and residue samples and the MCR content of these samples with more light distillates (less residual fraction) showed less MCR
HYDROCARBON WORLD VOLUME 4 ISSUE 1
43
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