K. MANTRI, J. K. REDDY, K. B. SIDHPURIA and R. V. JASRA, Reliance Industries
Ltd., Vadodara, Gujarat, India; and A. V. SAPRE, Reliance Industries Ltd., Mumbai, Maharashtra, India
Aromatics—specifically, benzene, toluene and xylenes (BTX)—are the basic building
blocks for most petrochemical derivatives and commodities chemicals. In terms
of volume, para-xylene occupies the top of the list of BTX, and almost the entire
production of para-xylene is consumed to produce polyester fiber. Naphtha is
reformed with a
continuous catalytic reforming (CCR) unit to convert paraffins and
naphthenes into an aromatics-rich stream (reformate). These aromatic streams
are further processed for the recovery of para-xylene (PX) from C8
aromatic streams, followed by transalkylation and disproportionation units to
produce an enriched p-xylene stream (FIG. 1).
With 4.3 MMtpy of PX production capacity, the authors’
company is the 2nd largest producer in the world. Aromatics produced from a platformer
invariably contains contaminants, including mono olefins, diolefins and
styrene. Unwanted olefins in reformate streams must be removed due to their
polymerization tendency, which leads to operational problems such as deactivation
of high-value catalysts and adsorbents in the downstream processes. The current
practice for removing olefins contaminants involves the use of acidic clay
treating process. The acidic sites on the clay surface catalyze the olefins to
react with the aromatics present via an alkylation reaction, producing heavy
hydrocarbons that are subsequently removed by fractional distillation.
Based on operational experience of
existing aromatics plants, the clay treating process has operational issues that include:
resolve these issues, the authors’ company has developed and commercialized an
olefins removal catalytic technologya. The heart of the technology is thermally
and mechanically stable high-performance catalyst—the proprietary catalytic technologya
has the requisite porosity architecture and surface acidity. The technology has
been developed to significantly extend the lifecycle of the catalyst compared
to existing clay catalysts. This catalyst reduces the amount of hazardous solid
waste generated with clay treaters. The performance provided by the new
technologya has led to significantly reduced operating cost as well
as opportunities to increase plant capacity.
A simplified process
flow diagram (PFD) of an aromatics complex for para-xylene production is shown
in FIG. 1.
Development of the new catalyst
nano porous alumino-silicate-based hybrid catalyst was developed1–3 and
commercialized at one of the authors’ company’s aromatics plants, providing a cost-effective
alternative to clays. Various milestones achieved during this development and
commercialization are depicted in FIG. 2.
process includes a novel catalytic process using regenerable catalyst for the removal
of olefins from a C8+ aromatics stream. The catalysta is
specially designed by controlling:
of the catalysta comprised the following steps:
The BI is defined as the number of milligrams (mg)
of bromine consumed by 100 grams (g) of hydrocarbon sample; it is used in
industry to measure the olefins content of aromatics containing hydrocarbon
samples using potentiometric titration.
Advantages of the new catalyst technologya
of the new catalyst technologya. After a
successful pilot plant trial using slipstream, a commercial trial of the
catalyst technologya was conducted at one of the authors’ company’s aromatics
plants. The catalyst was commercially produced—a snapshot of the finished catalyst is shown in
the left of the three images in FIG. 4. After rigorous testing of catalyst activity at the R&D
pilot plant, the catalyst was loaded in the commercial reactor (as shown in the
center and right image of FIG.
4) and the plant was commissioned.
heavy reformate was used as a feedstock. The feed composition is shown in TABLE 1. The heavy
reformate was a cut of full-range CCR reformate. This feedstock was processed
at a weight hourly space velocity (WHSV) = 2 h-1 over the new
catalysta at a temperature of 170°C–190°C
and pressure of 17 bar–22
Performance of the new catalysta. FIG. 5 shows the plot of the
BI at the inlet and outlet streams of the catalysta reactor vs. time
onstream (TOS) in days. As shown in FIG. 6, olefins conversion or BI reduction remains
> 95% from the start of the run; this trend of olefins conversion continues without
a reduction in olefins conversion activity, indicating that the performance of
the catalysta is excellent without deactivation and with expected
Quantity of olefins processed/loaded on
olefins removal efficiency of the catalysta can better be seen by
plotting olefins conversion vs. olefins processed or loaded over the catalysta
(FIG. 7). Olefins
loading is calculated by converting the BI into olefins concentration by taking
the molecular weights of olefins that are present in major quantity in the
total amount of olefins. The quantity of olefins loaded in kg or tonne (metric
t) over catalyst with TOS was calculated. Similarly, the amount of olefins
present at the outlet effluent was also calculated. From the plotted graph in FIG. 7, it is clearly
seen that although 195 metric t of olefins are loaded per metric t of catalysta,
the olefins conversion is still maintained at > 95%.
amount of olefins loaded over acid-treated clay is only 16 metric t of olefins
per metric t of clay material, where the olefin conversion dropped to 45%–50% corresponding to the
nearly exhausted capacity of clays and ready for replacement. In contrast, 195 metric
t of olefins are loaded per metric t of the new catalysta in a 14-mos
TOS and is continuing without degradation of olefins removal capacity. To date,
the catalyst’sa performance is 7 times higher than that of the conventional acidic clays while
maintaining an olefins conversion at > 95 %.
deactivation of catalyst is seen with TOS with continuous loading of olefins on
the catalyst. Generally, as the loading of olefins increases on the catalyst,
the gradual deactivation of catalyst is expected. Conversely, the catalyst
processa has not seen any reduction in the catalytic performance so
far—this is consistent
with the observations seen in the pilot plant as well as slipstream trial
discussed above. This confirms the high performance and robustness of the developed
Feed flow and catalyst bed temperature
of the catalyst technologya in a commercial reactor. FIG. 8 shows the plot of feed
flow and reaction temperature against days onstream. The actual operating
temperature of the clay treater is 170°C–175°C
and the WHSV is 1.4 h-1–2.5 h-1. As shown in FIG. 8, after 14 mos of TOS, the
temperature across the reactor bed is maintaining 170°C–180°C and flow holds steady at 16 m3/hr–30 m3/hr. So
far, no significant change in performance of the catalyst has been observed with
respect to feed flow during the run. This clearly indicates that the catalyst
is robust and can be utilized effectively even under high throughput, which may
have a positive impact on the economics of the process. An additional benefit
is that the single treatera has been providing the required BI
specifications since commissioning without switching to the swing bed.
Chemistry of olefins removal from aromatics
well known that the alkylation of aromatics with olefins over solid acid
catalyst occurs via the generally accepted carbenium ion mechanism illustrated
in FIG. 9.
On the basis of this mechanism, the olefins molecules adsorbed on the surface of
the zeolite gets protonated by the Bronsted or Lewis acid sites, thereby resulting
in the reduction of double bond to form a carbenium ion. The electrophilic
attack on the aromatic π-electrons
or olefinic π-electrons
leads to various reactions, such as cracking, oligomerization and alkylation.
acid sites favors alkylation and cracking, whereas Lewis’s acid sites favor oligomerization.
Only oligomerization may lead to polymerization and coke formation, which leads
to fast deactivation of the catalyst. Cracking reactions are favored by strong
acid sites. Alkylation reactions are favored by strong and medium strength of
acid sites of the catalyst. Oligomerization reactions are favored by weak acid
sites of the catalyst.
general, the activation energies of the above-mentioned reactions are in the
following order: Cracking > alkylation > oligomerization.
authors’ company’s catalysta is a nano porous aluminosilicate-based
material and can facilitate reactions such as cracking, alkylation and
oligomerizations. Although the operating conditions—specifically the reaction temperature—widely vary in each of
these reactions, all these reactions are possible under present operating
conditions over the catalyst for olefins removal processa from
aromatics streams. Therefore, it is obvious to consider these reactions in the
olefins removal process from BTX streams over the catalysta having strong
Bronsted acid sites and weak Lewis acid sites.
of the carbocations formed will be serving as an alkylating agent to the
alkylation reaction with aromatics, therefore resulting in alkylated aromatics
or heavier (C10 and C11 aromatics).
Alkylation mechanism. The first step in the
alkylation reaction is the olefins activation leading to a carbocation (FIG. 10). The
activation of the olefins occurs with the formation of carbenium ions by Bronsted
acid site proton of zeolite. The carbocation then undergoes a methyl shift to
yield a tertiary cation; this will happen if the carbon chain is branched.
Also, straight chain carbocation always rearranges to form more stable
technologya is a nano-porous aluminosilicate hybrid material-based catalyst
where the novelty lies in the synthesis procedures with inexpensive raw
materials. The formulation of the catalyst into a specially designed shape with
selected binders and additives achieves the desirable mechanical properties
without impacting reactions of the catalytic activity. The
specific catalyst shape
enhances mechanical strength and geometrical surface of the catalysta,
reducing the restriction in diffusion of reactants and products. This is
critical, especially for the liquid phase process. The novelty of the present
work also lies in designing the catalyst to achieve > 95% olefins conversion
without loss of xylene.
The following sections
will highlight key attributes of the authors’ company’s catalyst technologya.
waste and stable operation with increased safety of the operating staff, especially
during clay removal and replacement. The catalysta is highly
stable with high performance in olefins conversion activity, and is designed to
extend cycles of existing aromatics stream treaters and reduce or eliminate the
amount of hazardous clay solid waste generated. This can lead to significant
operating cost savings and help make existing plants more productive with
increased protection for downstream units. This catalyst requires a very short
dry-out time, and the proprietary knowledge developed includes synthesis and
forming of catalyst powder to specific shapes with requisite properties for
Unlike clay, the catalysta shows
very high thermal stability—for
olefins removal service, it provides higher cycle life, regenerability (in
contrast to non-regenerable clay) and economic options compared to commercial
alternatives. It also eliminates hazardous removal of clays by drilling,
removal and disposal, and exposure to operating personnel.
of the intangible benefits to be observed with commercialization of this catalysta
Longer operating cycles. The catalysta
achieves at least 12 times (as per pilot plant study) the lifetime as clay,
thereby lowering the number of catalyst change-overs and increasing productivity
due to a reduced number of shutdowns. Longer cycles reduce the risk of
exceeding downstream unit BI specifications and the resulting potential damage
to sensitive catalysts and adsorbents. The catalyst is regenerable and can be
reused multiple times, wherein solid waste generation is significantly reduced.
Additionally, the catalysta is less costly compared to commercial
alternatives with a shorter dry out period and no undesirable reactions.
life of clay is very short, huge quantities of used clay are generated from
petrochemicals plants. Removal from the reactors and disposal of used clay is a
big challenge. Increased care must be taken in the selection of landfills and
disposal facility sites because the leachates of clay may create water and soil
pollution in the long term. Replacing clay with the catalysta will
significantly reduce hazardous solid waste generation and handling. Because the
catalyst’s lifetime is very high and regenerable, there is essentially no solid
waste generation; therefore, this is an eco-friendly process for olefins removal
from aromatics streams.
Capital savings. Treaters loaded with the
catalysta will require fewer changeovers, significantly lowering operating
cost. In some cases, the longer cycle length provided by the process can avoid the
installation of additional clay treaters, which are used for further polishing the
BI to reach specifications before they are processed in subsequent petrochemicals
processes. The authors’ company’s technologya provides more stable
and trouble-free operation, as well as reduced labor-intensive and costly clay
changeover in the clay treater.
economic analysis comparison between the catalysta and the clay
catalyst considered the following points:
Based on the cost
avoidance observed by implementing the catalysta in olefins removal
process, the payback period is 15.7 mos.
Takeaways. The catalysta
is proven to be highly efficient in olefins removal activity without deactivation
even with high feed BI (BI: 1,000 mg/100 gm) under the same operating
conditions of current clay treaters. Based on the commercial operating performance
of the catalysta at the authors’ company’s site, run length is
predicted to be more than 10 yr. Apart from the economic benefit,
implementation of the catalysta will significantly reduce the hazardous
solid waste generation and disposal by an aromatics complex. HP
The authors want to thank their colleagues Jagannath
Das, Prakash Kumar, Vasant Warke and Leena Chaudhari for their support during
the development and commercialization of the technologya. Additionally,
the authors thank the RIL management for its support in developing and
implementing this technology in the operating plant.
a RIL’s Olefins Removal Catalytic (REL-ORCAT)
KSHUDIRAM MANTRI is
Group Lead, Zeolite Catalysis of Chemical Synthesis and Catalysis R&D, for Reliance
Industries Ltd. Dr. Mantri graduated from IIT, Kharagpur, and earned his PhD
from National Chemical Laboratory, Pune. He has served as a JSPS postdoctoral
fellow at Gifu University, Japan; and as a postdoctoral fellow at RMIT
University, Australia; Vrije Universiteit, Belgium; and National University of
Singapore, Singapore. Dr. Mantri has 22 yr of extensive experience in adsorption, heterogeneous and zeolite-based catalysis for chemical transformation, waste-to-wealth
value generation. He has experience in design, development, scale-up and
commercialization of catalysts and processes, and has published 48 research
articles and has 24 granted patents, including eight U.S. patents.
KRISHNA REDDY JAKKIDI is a Lead Research
Scientist in the department of Chemical Synthesis and Catalysis Research and
Development at Reliance Industries Ltd. in Vadodara and Mumbai, India. He holds a PhD in chemistry from
Indian Institute of Chemical Technology, Hyderabad, India and was a
Postdoctoral Fellow at Tokyo Institute of Technology, Tokyo, Japan. He
has 17 yr of research experience in heterogeneous catalysis, with a main focus
on the design and development of zeolite and metal oxide-based catalysts for
hydrocarbon transformations. Dr. Reddy also has experience in scale-up and
commercialization of catalysts and processes. He has published 20 research
articles in peer-reviewed journals and has been granted 10 patents.”
KALPESH SIDHPURIA is Lead Research
Scientist in the department of Chemical Synthesis and Catalysis Research and
Development at Reliance Industries Ltd. He received his PhD in chemistry from
VNSGU/CSMCRI and was a FCT Post-Doctoral Fellow at CICECO, University of
Aveiro, Portugal. He has 19 yr of extensive research experience in adsorption,
heterogeneous catalyst, metal oxides and zeolite catalysis, and new product
development. Dr. Sidhpuria also has experience in design, development, scale-up
and commercialization of adsorbents, catalysts and processes. He has
developed/scaled-up and commercialized different adsorbents (molecular sieves,
alumina, silica gel-based) and adsorptive processes in various plants. Dr.
Kalpesh has published 19 research articles in peer-reviewed journals, two book
chapters, and has been granted 15 patents.
RAKSH VIR JASRA, Senior
VP (R&D) at Reliance Industries Ltd., is a world-renowned catalysis, adsorption
and nanomaterials scientist. Dr. Jasra achieved his PhD from Indian Institute
of Delhi (IIT), Delhi, his post graduate degree from Delhi University, and was
a post-doctoral fellow at Imperial College of Science, Technology and Medicine
at London. He has developed 66 chemical processes, 27 of which were
commercialized in industry. He has published 325 research articles and has 288
granted patents, including 68 U.S. patents. Dr. Jasra is a Fellow of the Indian
National Science Academy and Indian National Academy of Engineering, and was
given the Lifetime Achievement Award by the Indian Chemical Society. Dr. Jasra is
also featured among the world’s top 2% of scientists in the field of physical
chemistry for the years 2020 and 2021 as per a study by Stanford University.
AJIT SAPRE, Group
President, R&D, Reliance Industries Ltd., has more than 40 yr of industrial
experience in the oil and gas, refining, petrochemicals, renewable energy,
sustainability and biotechnology industries. He has contributed to the
development and commercialization of several innovative technologies. Dr. Sapre
received his PhD in chemical engineering from the University of Delaware and an
MBA from Cornell University. He has published more than 100 technical papers,
one book and has more than 50 U.S. patents to his credit.