Boosting aromatics yield from waste plastics via synergetic process and catalyst design

by Danny Verboekend, Judy El Jablaoui and Kurt Du Mong of Zeopore Technologies NV, and Diana Ciolca and Niels J. Schenk of BioBTX B.V.

Introduction

Chemicals are the building blocks for the plethora of carbon-containing products that cater to our modern way of life. However, the chemical industry uses sizable amounts of fossil carbon that will, at a certain moment in the life cycle, end up in the environment as CO₂. This forms a large societal problem, causing losses in biodiversity and adverse health effects [1]. These hazards call for the adoption of technologies that accelerate the transition to sustainable chemical building blocks and promote the circularity of plastics. There are only seven chemical building blocks from where over 95% of all materials are made: methanol, ethylene, propylene, butenes, benzene, toluene, xylenes.

Chemical recycling has shown to be an essential technology in maximizing the circularity of plastics. The core component in chemical recycling regards the breaking down of the large polymer chains into smaller fractions, ideally back to the original monomers, typically using heat and an inert atmosphere, i.e. pyrolysis. Catalysts can be contacted with the waste plastic and combined with pyrolysis in several distinct manners, by either direct contacting of the waste plastics with the catalysts, or by integrated upgrading of the pyrolysis vapours.

In order to address the abundance of challenges that are common to waste plastic feedstocks catalysis, BioBTX developed the Integrated Cascading Catalytic Pyrolysis (ICCP) technology to convert biomass and plastic waste into BTX aromatics. The cascading design separates the pyrolysis and catalytic stages, allowing protection against contaminants and higher control over reaction conditions. Ultimately, this achieves a higher BTX yield and purity [2].

Like in the established oil refinery and adjacent chemical industry, zeolite catalysts hold the potential to become the workhorse of the plastic-waste refinery, for example in cracking reactions. Zeopore has a toolbox of proprietary mesoporization technologies, able to optimize the conversion efficiency of any zeolite catalyst on the market today. The introduction of mesoporosity in zeolite catalysts has demonstrated key to yield superior performance in virtually any catalytic reaction they have been applied in, including the chemical conversion of waste plastics [3].

Accordingly, the question arises: what would be the impact of the application of Zeopore’s technology in the BioBTX process?

Within this contribution we demonstrate an unprecedented performance boost based on the synergy between advanced pyrolysis processes and tailored catalyst design. Poly-olefinic and biomass waste streams are exposed to the ICCP process, developed by BioBTX, in which the resulting pyrolysis vapours are converted to aromatics via metal-based aromatization catalysts, designed by Zeopore. We show that by strategically implementing the aromatization catalysts in different scales in the pyrolysis process, and by tuning both the accessibility and the nature of the metal-site in the catalysts, unique yields of circular aromatics are achieved at a significantly reduced footprint.

Aromatization

Independent on the nature of the feedstock, aromatization reactions remain relevant to provide chemical building block for the chemical, fine, and pharmaceutical industries. Traditionally, aromatics are derived from naphtha or lights cracking, yet developments are also ongoing to yield aromatics from crude oil (crude to chemicals), and more recently also from natural (biomass) or synthetic (plastic) polymer waste streams (Figure 1).

Figure 1: Overview of the production and refining of fossil-based and circular aromatics [4].

Whereas naphtha cracking is mostly thermal, the conversion of crude oil to aromatics and polymers are best converted catalytically. In these processes, the most common catalysts are zeolite-based, typically ZSM-5 zeolites complemented with a metal, such as zinc or gallium, to add a (de)hydrogenation function. Also after the aromatization process, several catalytic conversions are present to maximize the eventual BTX yield, all of which best executed using mesoporous accessible zeolite catalysts [4].

Challenges in pyrolysis

The BioBTX Integrated Cascading Catalytic Pyrolysis (ICCP) technology is developed with the goal of making full carbon circularity possible [5]. Using a cascaded process design featuring two distinct steps (pyrolysis followed by catalytic upgrading of the pyrolysis vapours), enables the optimization of the energy input and the maximization of the BTX yields [2]. At the same time, the exposure of the catalysts to contaminants is strategically controlled, as to maximize catalyst life time. Within this contribution, the advanced zeolite catalysts are deployed in the sector targeted to upgrade the pyrolysis vapours (R2 in Figure 2).

Figure 2: illustration of the ICCP process from BioBTX [2].

Metal mesoporisation

Despite the established catalytic superiority, the industrial adaptation of accessible (mesoporous) zeolites has thus far been underwhelming. A probable cause for this may be the persistence of expensive ingredients and unscalable unit operations associated with the manufacture of mesoporous zeolites. For example, various undesired aspects complicate manufacture, such as large amounts of expensive organics, long hydrothermal stages, and hazardous combustions steps. Moreover, such processes are typically combined to sub-optimal material properties, such as strong Brønsted acidity, as was recently illustrated for hydrocracking [6].

Zeopore derives its right of existence by exclusively using scalable and cost-effective methods to make high-quality accessible zeolites. Moreover, the catalytic value of a simultaneous mesoporization with metal incorporation (Figure 3) was recently discovered, yielding unique catalysts and outstanding performance in hydro-isomerization and methanol to propylene [7]. Using this technology platform Zeopore has made a superior mesoporous Ga-containing ZSM-5 zeolite used in the below-described catalytic tests (Table 1).

Figure 3: Schematic summary of the Metal Mesoporization process of Zeopore [7].

Catalyst	Mesoporosity		Gallium
Standard	Limited		None
Standard/Ga	Limited		Introduced via impregnation
Zeopore/Ga	Ample: introduced via metal mesoporization		Introduced via metal mesoporization

Table 1: Properties of different ZSM-5 based catalysts.

High-throughput screening

The tunability of Zeopore’s technologies combined with the streamlined high-throughput testing facilities at BioBTX enabled to test a variety of zeolites in a short amount of time. Various compositions and porosities of zeolites were made and tested on sieved fractions on the gram scale, the performance of which is summarized in Figure 4.

Figure 4: Normalized BTX yields obtained on catalyst powders with PE feedstock in a high-throughput reactor.

The Standard zeolite yielded a BTX yield which was largely similar for the standard Ga-containing zeolite. Upon introduction of gallium, a pronounced shift towards benzene was evidenced. For the Zeopore/Ga sample, a similar shift can be observed, but much less pronounced. This suggests that the gallium species in this sample are of a distinct nature as compared to gallium introduced via impregnation.

Scale up, extrudates, and mini-plant

Based on the successful results in the screening phase, the Standard and Zeopore/Ga samples were converted into industrially-relevant catalyst shapes, that is, binder-containing extrudates. These extruded catalysts were tested on a mini-plant with a capacity of 200 g/h, being process-wise a downscaled version of a commercial plastic waste valorization plant.

Figure 5: Normalized BTX yields obtained on extruded catalysts on the miniplant on PE (left) a 50/50 PE/biomass mixture (right).

Figure 6: Normalized BTX yields obtained on extruded catalysts on the miniplant on PE (left) a 50/50 PE/biomass mixture (right).

Figure 5 reveals that the Zeopore/ Ga sample yielded a doubled amount of BTX. In the conversion of waste plastics, the co-processing of biomass offers some synergic opportunities, for example based on the oxygen content, and was therefore also evaluated. Also in this case, the mesoporous sample offered a doubled conversion as compared to the standard material. On the mini-plant, the selectivity to xylenes was significantly larger as compared to the screening phase. Moreover, the presence of mesoporosity and gallium appeared to specifically boost the selectivity to these valuable C8 aromatics (Figure 6, left). For PE mixed with biomass (Figure 6, right), the boost of aromatics was more equally spread over all BTX species. The differences between small scale and miniplant can be attributed to different reaction conditions such as batch vs continuous setup, WHSV and contact time.

Additional efforts were focused to vary reactions conditions to maximize for each catalyst the overall BTX yield. These efforts revealed that the Zeopore/Ga sample enables to boost the BTX level with an impressive 7 wt%. Importantly, this gain came at the expense of undesired gas formation, which was reduced by about 10 % relative to the standard catalyst.

Insights into reaction mechanism

In the aromatization of pyrolysis vapors using Ga/ZSM-5, the metal-component (gallium) acts as a dehydrogenation promoter, enhancing olefin aromatization, while the acidic ZSM-5 framework catalyzes oligomerization and cracking reactions, leading to increased aromatic yields from biomass and plastics [8].

Using the gas composition (Figure 7), we speculate that the origin of the superior performance of the Zeopore-derived catalysts is based on the enhancement of both dehydrogenation and cracking function via a proximity effect [9,10]. The enhancement of the external surface, leads to a closer proximity of the zeolitic acid site with the dehydrogenation potential and hydrogen transfer index (HTI) of the Ga sites, first, significantly improving the yield and selectivity of aromatics. This proximity effect is particularly pronounced for the Zeopore-derived Ga/zeolite, as the metal is introduced to the pure zeolite phase (Figure 3), and not to a mixed zeolite/binder phase, as would occur during the metal impregnation of a standard zeolite/alumina extrudate or pellet.

The presence of a proximity effect in the Zeopore/Ga catalyst relates well with the reduced gas make of the Zeopore/Ga catalysts: the increased conversion of olefins to aromatics reduces the amount of olefins left in the gas phase, lowering the overall yield of gas and concomitantly and a more paraffinic gas composition (Figure 7). The absence of butenes/butanes (C4s) from the Zeopore/Ga gas composition is striking, and is tentatively ascribed to the higher reactivity of C4s as compared to the smaller carbon numbers. The latter could in turn relate to the increased make of more alkylated C8 aromatics.

Figure 7: Weight-based gas composition obtained on extruded catalysts on the miniplant on PE.

Impact on emissions

Increasing the efficiency of chemical conversions can have a tremendous and often overlooked impact on emissions. A large amount of byproducts are undesired, such as light hydrocarbon and non-condensable  gases, especially methane. The latter are often flared or burnt off for heat recovery, that is, directly adding to the CO₂ footprint. By increasing the selectivity to desired products, and especially those not destined for fuels, the emissions per ton of desired product can be sizably reduced [11].

In the case of the Zeopore/Ga sample, not only was the overall gas production significantly lower, the composition of the gas (hydrogen + C1-C4) was shifted towards smaller carbon numbers and hydrogen. This meant that the relative abundance of carbon, hence potential CO₂, is significantly reduced. These two factors combined to the increased BTX yield imply that the selectivity-based CO₂ emission per gram of BTX obtained is nearly halved. This tremendous reduction is an excellent indication how catalyst design can help to reduce emissions in future waste, CO₂, or biomass-based refineries.

Outlook

The maximization of BTX yield from waste plastics pyrolysis vapours represents a milestone achievement, underlining the synergy between the ICCP process and of accessible zeolites. Further development, including understanding the nature of the material, stability testing, and catalyst shaping, is strived for to optimize manufacturing, optimize the business case, and trigger commercialization.

BioBTX aims to strategically use gathered insights and integrate catalyst design with optimization of plant currently being installed. Zeopore continuous to explore the application and commercialization in different configurations of waste plastics conversion, such as catalytic pyrolysis and py-oil upgrading. Herein, targeting also the other challenges such as improving the conversion degrees in catalytic pyrolysis, and dealing with feedstock impurities.

References

[1] M. L. Diamond et al., Exploring the planetary boundary for chemical pollution, Environment International, 78, 2015, 8-15.

[2] M. Van Akker et al., 2025, Full Utilization of Hard-to-Recycle Mixed Plastic Waste by Conversion toward Pyrolysis Oil and BTX Aromatics on a Pilot Scale. Energy & Fuels, 6438-6451.

[3] D. Serrano et al., Developing Advanced Catalysts for the Conversion of Polyolefinic Waste Plastics into Fuels and Chemicals, ACS Catal. 2012, 2, 9, 1924–1941.

[4] D. Verboekend, Enhancing C8+ aromatics conversion, Hydrocarbon Engineering, November 2024.

[5] https://www.sustainableplastics.com/news/biobtx-build-worlds-first-renewable-aromatics-plant.

[6] D. Verboekend, Maximising hydrocracker performance and middle distillate production, PTQ catalysis 2025, 53-57.

[7] D. Verboekend and M. d’Halluin, Benefits of simultaneous mesoporisation/metal incorporation, PTQ Catalysis 2023, 55-58.

[8] Y. Zheng et al., Journal of Analytical and Applied Pyrolysis, 126, 2017, 169-179, K. Qian et al., Fuel 357, 2024, 129781.

[9] C. M. Lok et al., Renewable and Sustainable Energy Reviews, 113, 2019, 109248.

[10] Guisnet et al., Aromatization of short chain alkanes on zeolite catalysts, Applied Catalysis A: General, 1992, 89, 1-30.

[11] D. Verboekend, Economic and environmental versatile technologies in refining, PTQ Q4 2025, 45-48.