T. Vilela and D. OTYUSKAYA, Avantium, Amsterdam, the
refining plays a significant role in the petrochemical refining industry. This refining
process requires a heterogeneous catalyst. A typical feature of this process is
that coke (or carbon) deposits are formed on the catalyst particles, resulting
in the gradual deactivation of the catalyst. To prevent catalyst deactivation
at the industrial scale, such refining processes employ moving-bed reactors in
which the catalyst moves through the reactor over time and passes through a
regeneration unit. Herein, the coke deposits are removed, and the catalyst is returned
to the reactor. Another important function of the regeneration unit is
maintaining catalyst acidity levels by means of chloride agent injection. Chloride
addition also plays an important role in redispersing the active metals. This
process is also known as the continuous catalytic regenerative (CCR) reforming
FIG. 1 shows a proprietary CCR platforming
processa, with four adiabatic reactors of different volumes and a
dedicated regenerator that burns off the carbon deposits from the catalysts, redisperses
the active metals and dries the catalyst before its reintroduction into the
FIG. 2 shows a different proprietary CCR
reforming technologyb. To ensure that catalyst activity in the
reactor is near-fresh catalyst, the catalyst circulation speed is maintained so that coke content on the spent catalyst
is less than 5 wt%. The catalyst (usually a platinum-tin/aluminum oxide variant)
is continuously circulated from the lead-reactor inlet to the lag-reactor
outlet. At the exit, the catalyst is severely deactivated due to coke formation.
High catalyst selectivity (C5+ yield) is always desired for a fixed research octane number (RON). The
stability of the selectivity is typically measured by the length and slope of
the stable C5+ yield output before the temperature rises sharply.
The authors’ company provides
independent catalyst testing to investigate and compare the performance of
various catalysts. Catalyst testing is often conducted in small reactors, with
reactor volumes of a few cubic centimeters. Such small reactors cannot be
practically operated as moving-bed reactors; therefore,
these tests are carried out in fixed-bed reactors. For this, a proven
high-throughput, 16-parallel-reactors micro-pilot plant is used (FIG. 3).
formation of coke deposits, which are not burned off like in a moving-bed
reactor, makes it challenging to translate results from small lab-scale tests
using fixed-bed reactors to factory-scale moving-bed systems. Moreover, since the
partial catalyst deactivation not only results in lower yield (as expressed by
C5+) but also in decreasing RON of the product stream (which are
generally offset by increasing reactor temperature), achieving a high and
stable RON for the product stream over time requires constant parameter
fine-tuning. The iso-RON operation is achieved by using an automated feedback
loop between the gas chromatography (GC) analysis of the effluent and the
reactor’s temperature, the latter of which is continuously adjusted.
the authors’ company developed a new pilot plant to evaluate—on a small scale (with
reactors of a few cubic centimeters in volume)—the performance of multiple CCR catalysts.
This process considers the coke or carbon deposits formed on the catalyst
particles and their effect on RON and C5+ yields. In this innovative
testing process, catalysts are tested in a parallel fixed-bed system at the temperature
required to achieve a desired RON and C5+ yield at different
catalyst coke contents. This enables the direct comparison of multiple
catalysts at identical coke levels, and determines the effects caused by coking
by means of data interpolation.
article provides the test results used as an example in the new process to
showcase an independent test to support a refinery with its catalyst selection
commercial naphtha CCR catalysts (Catalysts A–C) were evaluated in a system of 16
parallel fixed-bed reactors, with the reactors having a diameter of 2 mm–2.6 mm.
Each reactor has an independent temperature controller that enables individual
reactors to operate at a constant RON. FIG. 3 shows a schematic of the testing
equipment employing the authors’ company’s proprietary technologyc,
which provides precise control of process conditions (i.e., temperature,
For each catalyst, 0.6 ml of material was loaded in three
identical reactors. In total, 12 reactors were operated simultaneously in a
single run. At any point in time, all 12 reactors saw the same pressure and
hydrogen flowrate. The operating conditions for this example are presented in TABLE 1.
The naphtha feeds were dried by passing them over a bed
of molecular sieve 3A calcined for 12 hr at 280°C. The feed was prepared in
batches (typically 1.5 kg) and stored under inert conditions for the duration
of the project.
Once the feed is thoroughly dried, the water:chlorine
ratio can be adjusted, following the client’s requirements (to be discussed
upfront). Additional components (sulfur or nitrogen) can also be added, if
For the spiking of the feed, dimethyl-disulfide is typically
used to add sulfur, tert-butylalcohol is used to add water, tert-butylamine is
used to add nitrogen, and tert-butylchloride is used to add chlorine.
The effluent product was fully analyzed by GC. The
product composition (including the C5+ yield, total aromatic yield
and hydrogen yield) and properties (RON) were determined from the combination
of the individual components quantified by GC. Specifically, the RON value was
determined from the product composition, based on an empirical relationship
previously derived between the composition of catalytically reformed naphtha
samples, as determined by GC, and actual engine knock-test results.
Each reactor was
sequentially analyzed by the GC with a frequency of ca. 9 hr between two
measurements of the same reactor. After each measurement, an algorithm based on
the proportional-integral-derivative (PID) principle automatically adjusted the
temperature of the corresponding reactor so that the resulting RON value would
continuously approach the RON target.
During the naphtha reforming test, each of the three
reactors were consecutively taken offstream at three specific times. Each
reactor was sequentially taken offstream by interrupting the flow of the liquid
(naphtha) and lowering the reactor temperature to ca. 360°C to deliberately
stop naphtha reforming reactions and coke formation (i.e., to fix coke content for
each reactor at a given time-onstream). This procedure was done to create three
catalyst performance data sets at three different coke contents. All reactors
continued to see the same reactor pressure and hydrogen flowrates.
GC analysis of the offstream reactors confirmed that no
more catalytically reformed naphtha was being produced from the reactors that
were taken offstream.
The test ended when the last
reactors were taken offstream. At this point, the spent catalysts were
individually removed from the reactors to be analyzed for coke content.
Coke analysis. An
analysis of the coke proceeded by crushing all the catalyst beads per reactor
into a fine, homogeneous powder. Powder samples of ca. 15 mg–20 mg were loaded
in an alumina crucible analyzed by thermogravimetric analysis (TGA). This was achieved
by applying a constant flow of air over each sample and increasing the temperature
at a rate of 10°C/min from room temperature to 800°C. Two samples were analyzed
The resulting weight loss recorded during the analysis
corresponded to the amount of coke that was burned off from the catalyst
surface after correction for the usual amount of water loss and annealing that
typically occurs with these materials. Catalyst weight loss between 260°C and 550°C
was determined to correspond to coke removal, since any weight loss below 260°C
is water loss. The annealing loss was corrected by subtracting the curve of a
fresh sample of the same catalyst.
performance indicators. Key
catalyst performance indicators (including reactor temperature, C5+
yield, aromatic yield and hydrogen produced) were fitted for each catalyst and
variable across all the data points measured in all three reactors
simultaneously, with a polynomial function with time onstream (FIG. 4).
buildup. Since the amount of coke deposited per
reactor can only be determined after terminating the test, this innovative test
design requires multiple datapoints for the coke deposition—i.e., time relationships
corresponding to several reactors loaded with the same catalyst that are
operated at different times onstream. In this test, three reactors per catalyst
were used, resulting in three different coke contents at the end of the entire
coke buildup on the catalysts usually follows a power function with time
onstream if the catalyst deactivation is not left to continue beyond what is
typically considered reasonable. The three points of coke with time onstream,
which were obtained for each catalyst by post-mortem TGA analysis, were calculated,
and the equations listed in TABLE 2 were determined. The results are shown in FIG. 5 (experimental
coke points with minimum-maximum error bars from the duplicate coke
measurements, fitted curves, and a horizontal line that indicates the coke
target for interpolation). The time onstream corresponding to the coke target (here, 3.75 wt%) was calculated from these equations.
The target coke content was not reached at the same time for all the catalysts.
FIG. 5 provides the results with time onstream
for all three catalysts (each line is a reactor and corresponds to a coke
Interpolation of the
experimental data. By
comparing various effects or properties over time (e.g., C5+ yield,
temperature required to maintain constant RON, coke content), additional relationships
can be derived using interpolation, such as yield vs. coke content, temperature
vs. coke content, or performance at a fixed-coke content. This is desired,
since refineries often operate their CCR units at a set coke content. Therefore,
the estimation process, according to this innovative test design, provides a
reliable comparison of various catalysts under the conditions that the CCR unit
The catalyst performance indicators (reactor temperature,
C5+ yield, aromatic yield, hydrogen produced) were fitted for each
catalyst and were variable across all the data points measured in all three
reactors simultaneously (per catalyst), with a polynomial function with time
onstream (FIG. 6).
For each catalyst, the activity (reactor temperature) and
yields were interpolated at the time onstream required to reach the target coke
content, as determined earlier. FIG. 6 shows the test data, with the fitted curves overlaid.
The interpolation point is displayed on the curve with the 95% prediction
interval derived from the fit.
Catalyst performance was finally compared at the same coke
content by representing the interpolated yields vs. the interpolated activity
(reactor temperature), as shown in FIG. 7.
In FIG. 7, at the same time
to coke target, the difference in performance
between the three catalysts can be clearly seen.
innovative test design enables refiners to compare the performance of various CCR
catalysts at a given coke content and for the reactor temperature that would go
with this in the CCR unit. This test design allows small-scale
testing of naphtha reforming catalysts in fixed-bed reactors, despite coke
formation over the reaction time (which differs per catalyst)—thus providing an
estimation of a catalyst’s performance in the moving-bed CCR reactors, even
though such reactors operate at a steady-state coke deposit percentage. HP
Platforming is licensed by Honeywell UOP
Axens’ Octanizing™/Aromizing™ technology
c Avantium’s Flowrence
The authors would like to acknowledge Nicolas Popoff, the
inventor of this innovative test design to compare naphtha reforming catalysts.
This work is the culmination of his dedication and collaboration with all major
catalyst suppliers to provide customers with meaningful test results that
enable fact-based decisions and improve catalyst selection.
TIAGO VILELA leads the Refinery Catalyst Testing
(RCT) global services for Avantium. He has more than 20 yr of experience in
engineering, project management, management consultancy and business
development. Dr. Vilela earned an MS degree in chemical engineering from the
University of Aveiro in Portugal, and his PhD in engineering from Delft
University of Technology in the Netherlands. He can be contacted at Tiago.Vilela@avantium.com.
DARIA OTYUSKAYA leads
the naphtha reforming catalyst testing programs for Avantium. She has more than
10 yr of experience in catalyst testing, data modeling, and research and
development project management. Dr. Otyuskaya earned an MS degree in chemical
engineering from the D. Mendeleev University of Chemical Technology of Russia,
and a PhD from Ghent University in Belgium.