November
2016
HYDROCARBON
ENGINEERING
88
phenomenon is caused by free water and not dissolved
water. Therefore, the content of H
2
O should only be a
concern when it reaches half of the value of the
concentration corresponding to the solubility of H
2
O
in the stream to be treated.
Typically, levels of H
2
O at ≤500 ppm-wt do not
cause this type of issue (far from the values normally
found in the raffinate stream).
Clays
Essentially, F-24X is an evolution of F-24. F-24X has a
higher density than the F-24, which allows the loading
of an additional quantity of clay (about 25 wt%, when
compared with the F-24) for the same available
volume. Additionally, F-24X is claimed to have a higher
catalytic activity compared with F-24 (about 10%).
In December 2014, the loading of F-24X was carried
out for the first time with a mixed bed (11 t F-24 + 19 t
F-24X). Currently, four cycles supplemented with F-24X
for the production of solvents have been completed.
Comparative assessment of the clays
The following section provides a comparative
evaluation of F-24 and F-24X, with respect to three
factors: olefin saturation capacity (expressed in
Kg Br/kg clay); energy consumption (in kg of VIP/m
3
raffinate); and treatment costs (
€
/m
3
raffinate).
It is also worth noting that, for comparison
purposes, all production runs of hexane were selected
from January 2013. For statistical purposes, Run 4, in
2013, was omitted (due to suspicions that the clay was
contaminated with C9s, causing a very significant
reduction of the clay lifetime), as well as Run 1 from
2015 (it was necessary to significantly anticipate the
final portion of the cycle due to the saturation of the
clay, associated with the treatment of the BT cut).
Thus, for the F-24, a total of four runs were considered
and, for the F-24X, a total of three runs were
considered, including the run with mixed bed
(11 t F-24 + 19 t F-24X).
Saturation capacity of olefins
Figure 4 shows the saturation capacity of the olefins by
F-24 and F-24-X (expressed in kg Br/kg clay). From
observing the figure, it can be seen that, on average,
F-24X has a greater olefin saturation capacity
compared with that of F-24 (about 5 kg Br/kg clay).
This difference represents an increase in capacity in
the order of 40% (higher than the 10% claimed by BASF
as a minimum improvement).
However, it is important to note that there are
particularities in the production process. The cycle
time of the clays are significantly affected by several
factors, namely:
n
n
Simultaneous production of hexane and heptane
(operation with higher severity to meet the
heptane specification).
n
n
Interruption of the run of solvents due to C9s
production (may cause C9s contamination on the
subsequent startup of the clays in service).
n
n
The maximum capacity of the clay may not be used
because it reached the final stage of the cycle in
the other bed (in operation with the BT cut),
making it necessary to anticipate the replacement
of the bed.
As it is very difficult to estimate and quantify the
impact of each of these factors on each run, it is
assumed that the statistically treated data may be
affected with a significant percentage of error;
therefore, the quantified benefits (about 5 kg Br/kg
clay) may not accurately reflect the reality.
Energy consumption
Figure 5 shows energy consumption data
(kg steam/t raffinate) for F-24 and F-24X. In the figure
it appears that, on average, the energy consumption
associated with the F-24X is lower than the energy
consumption associated with the F-24 (approximately
11 kg steam/t raffinate). This difference means a
decrease in steam consumption by approximately 8%
wt. This fact is a consequence of the lower saturation
rate of the F-24X, which implies less pronounced
temperature rises over the run.
Treatment costs
Figure 6 shows the cost of treatment (
€
/raffinate t)
associated with the use of F-24 and F-24X. In the
treatment cost, only the cost of clay (purchase cost +
hand labour for bed replacement) has been considered,
as energy costs are much less significant and the price
of steam has undergone considerable fluctuations
(indexed to the price of fuel gas/natural gas), which
could distort some economic gains.
Looking at Figure 7, it appears that, on average,
treatment costs associated with the use of F-24X clay
are lower than the treatment costs associated with the
use of F-24, and this difference is reflected in
approximately
€
5/t of refined product. This difference
is due to the higher olefin saturation capacity of F-24X.
Conclusion
F-24X has a greater capacity for the saturation of
olefins than F-24, and this difference is translated into
approximately 5 kg Br/kg clay, which then translates to
a capacity increase of around 40%.
The energy consumption associated with the use of
F-24X is lower than the energy consumption associated
with the use of F-24, and this difference is reflected in
about 11 kg steam/t raffinate, which leads to a lower
steam consumption of about 8 wt%.
The treatment costs provided by the use of F-24X
are lower than the costs of those provided by the use
of F-24. This difference is quantified at around
€
5/refined t.
As the aromatic and cycloaliphatic feed streams in
refineries differ, the benefits of the new mineral
catalyst may vary from unit to unit. Nevertheless, due
to good experience in laboratory tests and in several
large units, significant improvements in unit lifetime
and treatment costs can be expected.
