Development and commercialization of an olefins removal catalytic technology

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:

1. Shorter cycle life—the average life of the clay is 2 mos–3 mos
2. Longer clay replacement period
3. Safety challenges during clay removal
4. Disposal of large quantities of spent clay poses serious environmental challenges
5. Loss of C₈ aromatics yields through additional heavier generation
6. Spikes in outlet bromine index of single clay treater during clay change-over.

To resolve these issues, the authors’ company has developed and commercialized an olefins removal catalytic technology^a. The heart of the technology is thermally and mechanically stable high-performance catalyst—the proprietary catalytic technology^a 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 technology^a 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 technology^a. The nano porous alumino-silicate-based hybrid catalyst was developed^1–3 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.

The process includes a novel catalytic process using regenerable catalyst for the removal of olefins from a C₈+ aromatics stream. The catalyst^a is specially designed by controlling:

1. A micro-meso porosity architecture to facilitate diffusion of reactant and product molecules
2. Surface acidity for selective alkylation reaction of olefins with aromatics
3. Thermal and mechanical stability to allow regeneration.

The development of the catalyst^a comprised the following steps:

1. Low-cost catalyst recipe from inexpensive, easily available raw materials
2. Establishing the preparation procedure and suitable scaling-up
3. Standardizing formulation and shaping to form extrudates
4. Producing and supplying 10 kg of the finished catalyst for an onsite slipstream trial at one of the aromatics plants under commercial operating conditions
5. Pilot plant was commissioned to treat combined streams of platforming deheptanizer bottoms reformate; FIG. 3 shows the set-up and representative performance data
6. Trial was in operation for nearly 5 yr with significant reduction in Bromine Index (BI) at the outlet of the reactor
7. Based on this pilot plant trial and laboratory experimental data, the life of the catalyst^a was estimated to be at least 12 times that of clay.

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 technology^a include:

1. Very long operating cycles, at least 12 times longer than that of clay with reduced solid waste
2. Reduced number of shutdowns in clay treaters during clay change-over
3. Increased life of clay in lag clay treater (in lead-lag system)
4. Eco-friendly and shorter dry-out process
5. Capital savings: Retrofit with drop-in catalyst
6. Simple fixed-bed process
7. No benzene production as byproduct and no loss of C₈ aromatics
8. No styrene breakthrough at the end of run (EOR).

Commercialization of the new catalyst technology^a. After a successful pilot plant trial using slipstream, a commercial trial of the catalyst technology^a 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.

A 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 catalyst^a at a temperature of 170°C–190°C and pressure of 17 bar–22 bar.

Performance of the new catalyst^a. FIG. 5 shows the plot of the BI at the inlet and outlet streams of the catalyst^a 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 catalyst^a is excellent without deactivation and with expected product distribution.

Quantity of olefins processed/loaded on catalyst^a. The olefins removal efficiency of the catalyst^a can better be seen by plotting olefins conversion vs. olefins processed or loaded over the catalyst^a (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 catalyst^a, the olefins conversion is still maintained at > 95%.

The 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 catalyst^a in a 14-mos TOS and is continuing without degradation of olefins removal capacity. To date, the catalyst’s^a performance is 7 times higher than that of the conventional acidic clays while maintaining an olefins conversion at > 95 %.

No 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 process^a 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 catalyst^a.

Feed flow and catalyst bed temperature of the catalyst technology^a 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 treater^a has been providing the required BI specifications since commissioning without switching to the swing bed.

Chemistry of olefins removal from aromatics stream. It is 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.

Bronsted 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.

In general, the activation energies of the above-mentioned reactions are in the following order: Cracking > alkylation > oligomerization.

The authors’ company’s catalyst^a 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 process^a from aromatics streams. Therefore, it is obvious to consider these reactions in the olefins removal process from BTX streams over the catalyst^a having strong Bronsted acid sites and weak Lewis acid sites.

Most 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 carbocation.

The technology^a 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 catalyst^a, 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.

KEY BENEFITS

The following sections will highlight key attributes of the authors’ company’s catalyst technology^a.

Reduced solid waste and stable operation with increased safety of the operating staff, especially during clay removal and replacement. The catalyst^a 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 commercial applications.

Unlike clay, the catalyst^a 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.

Some of the intangible benefits to be observed with commercialization of this catalyst^a include:

1. Minimization of intensive hazardous labor-oriented clay changeover
2. Steady process (no spikes in BI during clay changeover)
3. Opens options for many more commercial applications
4. Built up capability of scale-up and manufacturing of highly potential cataylst commercially.

Longer operating cycles. The catalyst^a 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 catalyst^a is less costly compared to commercial alternatives with a shorter dry out period and no undesirable reactions.

Eco-friendly process. As the 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 catalyst^a 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 catalyst^a 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 technology^a provides more stable and trouble-free operation, as well as reduced labor-intensive and costly clay changeover in the clay treater.

An economic analysis comparison between the catalyst^a and the clay catalyst considered the following points:

1. A clay-based catalyst unit consists of two swing vessels installed in parallel as lead-lag operation. When clay in lead gets exhausted, lag will become lead; deactivated clay is replaced by fresh clay and that clay treater will be acting as a lag.
2. In the case of the process^a, one treater is filled with the catalyst^a and the other treater is filled with acid treated clay, for polishing the BI.
3. In the clay-based olefins removal process, two parallel clay treaters are each filled with acid treated clay.
4. The average inlet feed BI is 1,000 mg/100 g, which is coming from the upstream platformer. The specified outlet feed BI in the lag will be < 20 mg/100g. In both cases, the design space velocity WHSV is 2 h^-1–2.5 h^-1 with a feed inlet temperature of 170°C–180°C.
5. The payback for the catalyst^a is calculated assuming a 120-mos evaluation period.
6. The initial cycle length of fresh catalyst^a is expected to be at least 3 yr—it is then regenerated a minimum of two times to provide at least 10 yr of overall life. In contrast, clay-based catalyst operation requires change-over for every 2 mos; therefore, 60 change-overs of clay would be needed in 10 yr. For the catalyst^a, only two times ex-situ regeneration might be required in 10 yr.

Based on the cost avoidance observed by implementing the catalyst^a in olefins removal process, the payback period is 15.7 mos.

Takeaways. The catalyst^a 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 catalyst^a at the authors’ company’s site, run length is predicted to be more than 10 yr. Apart from the economic benefit, implementation of the catalyst^a will significantly reduce the hazardous solid waste generation and disposal by an aromatics complex. HP

ACKNOWLEDGEMENT

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 technology^a. Additionally, the authors thank the RIL management for its support in developing and implementing this technology in the operating plant.

NOTES

^a RIL’s Olefins Removal Catalytic (REL-ORCAT) Technology

LITERATURE CITED

1. Reddy, J. K., et al., “Synthesis of Ce‑MCM‑22 and its enhanced catalytic performance for the removal of olefins from aromatic stream,” Journal of Porous Materials, Vol. 27 (2020).
2. Reddy, J. K., et al., “Zeolite-based catalysts for the removal of trace olefins from aromatic streams,” Applied Petrochemical Research, Vol. 10, 2020.
3. J.K. Reddy, et al., “Effect of particle size of ZSM-5 zeolite on catalytic performance,” Catalysis in Green Chemistry and Engineering, Vol. 2, 2019.

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.