Search Results (71)

The transition toward lower-carbon polyolefin manufacturing requires evaluating whether renewable hydrogen can be used in industrial polypropylene production while maintaining acceptable process operation and product quality. In this study, an industrial gas-phase polypropylene production campaign that used electrolytic hydrogen was assessed using statistical and multivariate analyses. A dataset comprising 1441 process observations and more than 100 laboratory measurements was analyzed to characterize process variability, catalyst-feed stability, fouling behavior, and polypropylene quality. The monitored variables included the H₂/C₃, triethylaluminum-to-titanium selectivity-control-agent-to-titanium (TEAL/Ti), SCA/Ti, and TEAL/SCA ratios, production rate, reactor pressure, distributor-plate pressure drop, recycle-system variables, and fouling indicators. Product quality was evaluated through melt flow index, xylene solubles, bulk density, and residual catalyst species. Descriptive statistics, temporal analysis of variance, Pearson correlation analysis, and principal component analysis were applied to identify the main sources of operational variability and their relationships with product quality. During the evaluated campaign, the process maintained an average production rate of 30.62 ± 0.69 t h⁻¹, with low variability in the principal catalyst-feed ratios. The polypropylene exhibited an average melt flow index of 2.10 ± 0.11 g/10 min and a xylene-soluble content of 1.19 ± 0.08 wt.%, both within the specifications considered for the commercial grade produced. Temporal analysis of variance identified catalyst ratios, hydrogen utilization, and production rate as the variables with the largest temporal effects, whereas the distributor-plate fouling factor showed comparatively limited variation. The first two principal components explained 58.99% of the total process variance, with hydrogen utilization, catalyst-related variables, reactor pressure, and space–time yield among the dominant contributors. These results provide industrial-scale evidence that electrolytic hydrogen can be integrated into the investigated polypropylene process while maintaining stable operation and specification-compliant product quality during the evaluated period. However, because no parallel or matched campaign using fossil-derived hydrogen was available under the same plant, catalyst, grade, and operating conditions, the present results should not be interpreted as demonstrating full equivalence or direct replacement of conventional hydrogen. Instead, the study establishes an operational baseline and a multivariate monitoring framework for future comparative validation of the use of renewable hydrogen in polyolefin manufacturing. Full article

Polyolefin elastomers (POEs) produced by ethylene/α-olefin copolymerization are indispensable for high-end applications such as photovoltaic encapsulation, precision microelectronic protection, advanced foamed footwear, and automotive lightweight components. α-Diimine nickel catalysts that operate through a chain-walking mechanism convert ethylene as the sole feedstock into highly branched polyethylene elastomers, eliminating the need for expensive comonomers. This review systematically analyzes α-diimine nickel complexes developed in recent years via modulation of ligand steric hindrance, electronic effects, and backbone rigidity, and provides a quantitative comparison of their catalytic performance. The compiled data reveal that the catalytic activities span 10⁴–10⁷ g PE (mol Ni)⁻¹ h⁻¹, the molecular weights range from 10⁴ to 10⁶ g mol⁻¹, and the polydispersity indices (PDIs) can be tuned between 1.2 and 29.3, affording polyethylenes with branching densities from 2 to over 186 branches per 1000 carbons. These structural parameters directly govern the mechanical flexibility, elastic recovery, thermal properties, and processability in injection molding, foam extrusion, and film blowing, thus dictating the materials’ suitability for the aforementioned high-value applications. By establishing clear structure–performance relationships, this review offers forward-looking guidance for the industrial scale-up and catalyst design of polyethylene elastomers produced exclusively from ethylene. Full article

Managing polymer waste, primarily polyolefins—low- and high-density polyethylene and polypropylene—is a critical challenge in the transition to a low-carbon, circular economy. Traditional approaches (landfilling and incineration) are inconsistent with sustainable development principles and increasingly stringent extended producer responsibility regulations, while chemical recycling, particularly catalytic pyrolysis, is considered a key technology for returning hydrocarbon feedstocks to the production cycle. This mini-review systematizes and analyzes current advances in the catalytic pyrolysis of polyethylene and polypropylene. An algorithm for selecting a recycling route for polyolefin-containing waste based on its composition, degree of degradation, and the presence of hazardous additives is proposed. Existing and planned industrial projects in the field of chemical recycling of polyolefins are assessed, and challenges and prospects for technology commercialization are outlined. It is demonstrated that catalytic pyrolysis has the potential to become a key element of a circular economy for plastics, ensuring decarbonization and resource conservation with further optimization of catalysts and process flowsheets. Full article

Chemical recycling of polyolefins is essential to mitigate plastic waste accumulation and promote circular economy strategies. Among the various chemical recycling pathways, catalytic pyrolysis, tandem catalyst systems, ethenolysis, hydrocracking, and hydrogenolysis have emerged as promising approaches for converting polyolefin waste into valuable hydrocarbons, including gaseous, liquid, and solid products. This review provides a comprehensive survey of recent research on these methodologies, with a particular focus on the production of light gaseous hydrocarbons (C2–C4), bypassing the intermediate pyrolysis oil stage, potentially reducing contamination issues and simplifying downstream processing. In contrast to conventional reviews focused primarily on liquid products, the present work emphasizes strategies for enhancing the selective production of light gaseous hydrocarbons due to their potential application in circular monomer manufacturing. Aspects such as catalyst selection, reaction conditions, and product distribution are analyzed. Additionally, the current Technology Readiness Level (TRL) of the studied processes and their relative advantages, limitations, and perspectives for industrial applications are discussed. The analysis highlights catalytic pyrolysis with zeolites as the most mature and scalable technological alternative for manufacture of light compounds directly from polyolefin waste, while tandem catalyst systems and ethenolysis constitute promising but still emerging alternatives for targeted gas production. Full article

This review summarizes recent applications of nuclear magnetic resonance (NMR) in olefin polymerization catalysis. Due to its capability for quantitative characterization of molecular structures and in situ study, NMR is employed to study the structure of catalysts, and to trace catalyst/cocatalyst interactions, the evolution of active species, monomer insertion, and chain-end formation. This review emphasizes the activation mechanisms of molecular catalysts, ion-pair structures, and the measurement of kinetics. It also discusses the potential applications of in situ multinuclear NMR and isotope labeling technologies in olefin polymerization catalysis studies. Full article

The development of polyolefin from bio-renewables has been considered an important subject in terms of circular economy. In this study, exploring the possibility of β-myrcene (MY) incorporation in propene copolymerization has been studied in the presence of various catalysts: phenoxide-modified half-titanocene, Cp’TiCl₂(O-2,6-ⁱPr₂-4-C₆H₃) [Cp’ = Cp* (C₅Me₅), Me₃SiC₅H₄], and ketimide-modified half-titanicene, Cp’TiCl₂(N=C^tBu₂) (Cp’ = Cp*, Cp). Among the complexes tested, the permethylated Cp* catalysts, Cp*TiCl₂(O-2,6-ⁱPr₂-4-C₆H₃) and Cp*TiCl₂(N=C^tBu₂), exhibited moderate catalytic activities in the copolymerizations, affording the copolymers up to 3 mol% MY incorporation. The other catalysts showed negligible activity in the attempted copolymerizations. The resulting copolymers were amorphous and possessed sole glass transition temperatures (T_g), suggesting uniform compositions; the T_g values decreased with increasing comonomer (MY) content, reaching values as low as −17 °C. The results introduce valuable insights into the structure–property relationships of myrcene-based copolymers and pave the way for the future designs of tailored molecular catalysts for the synthesis of biobased elastomers. Full article

The fast growth of the aviation sector has intensified the need for sustainable alternatives to conventional fossil-based jet fuels. Sustainable aviation fuel (SAF) has emerged as one of the most promising strategies to reduce greenhouse gas emissions while remaining compatible with existing aviation infrastructure. Among the different feedstocks explored for SAF production, lipid-based resources such as vegetable oils, animal fats, and waste cooking oil have received considerable attention due to their high content of triglycerides and free fatty acids. Additionally, the increasing generation of plastic waste has stimulated interest in its catalytic valorization as an alternative carbon source for hydrocarbon fuel production. This mini-review summarizes recent advances in catalytic pathways for producing jet-fuel-range hydrocarbons (C₈–C₁₆) from lipid-based feedstocks and polyolefins. Particular emphasis is given on hydroprocessing reactions, including deoxygenation, cracking, and isomerization, which are essential to adjust fuel properties and meet aviation specifications. In this context, bifunctional heterogeneous catalysts play a crucial role, particularly regarding the influence of the metal phase and catalyst support on catalytic activity and stability. Different support classes, including metal oxides, mesoporous silicas, and zeolites, are discussed. Carbon-based materials, especially carbon nanotubes (CNT), are also highlighted due to their outstanding chemical and textural properties. Full article

In addition to the inherent challenges associated with controlling polymerization reactors, the “Sclairtech” technology for the production of Linear Low-Density PolyEthylene (LLDPE) presents specific characteristics (e.g., high temperature and pressure and a residence time in the reactor of less than 1 min) which add further difficulties to the effective control of the main quality parameters of the polymer produced. This work presents a strategy for implementing advanced control in a real LLDPE production unit (“Sclairtech” technology) followed by a systematic evaluation of the economic benefits in accordance with best international practices. Melt Index (MI), density and conversion were considered as controlled variables. The methodology for implementing advanced control involved analysis by resin classes (rotational molding, low-density injection, octene film and high-density injection) and effective contributions such as an innovative strategy for reactor temperature control. The proposed control strategy is capable of efficiently addressing two of the main problems associated with “Sclairtech” technology, namely, the generation of out-of-specification product during grade transitions and wide specification ranges. The benefits analysis involved the use of real process data, a statistical analysis of key variables to identify the dispersion and percentage of out-of-specification products, and the calculation of the net present value of financial indicators capable of validating the investment. Regarding quantitative outcomes, an annual gain of US$ 791,812 was estimated, with US$ 494,883 coming from the reduction in catalyst consumption and US$ 296,929 from other sources (reduction in out-of-specification product and production losses associated with grade transitions). Full article

Polyolefins are widely used polymers, with an annual global production of hundreds of millions of tons. Because they are the simplest hydrocarbon polymers, their intrinsic non-polar properties limit further applications. Coordination–insertion copolymerization of an olefin with other monomers, mediated by transition metal catalysts, is the most efficient way to synthesize polar and multi-functionalized polyolefins with enhanced material performance. Previous reviews have primarily focused on the structural design of a specific catalyst or on binary copolymerization of an olefin with a particular comonomer. However, the transition-metal-catalyzed ternary coordination–insertion polymerization of olefin monomers remains scarce. In this contribution, early transition-metal catalysts, such as Ti, Zr, Hf, and V, are employed for the terpolymerization of all-hydrocarbon or non-polar monomers to access advanced polyolefin materials with high performance. By contrast, late transition metal catalysts based on Ni and Pd, as well as rare-earth metal catalysts ligated by Sc and Y, enable the terpolymerization of olefins with a variety of heteroatom-containing monomers. Their strong tolerance empowers the development of polyolefins with multiple functionalities, thereby distinguishing these systems. The catalyst structure, catalytic process, and mechanism studies are summarized, along with the microstructure and functionality of the polymerization products, by classifying the types of termonomers employed. Full article

Development of new polymers that cannot be achieved by using conventional catalysts has been the central research objective, and copolymerization is an effective strategy to modify the materials’ (thermal, physical, mechanical and electronic) properties. Modified half-titanocenes, Cp’TiX₂(Y) (Cp’ = cyclopentadienyl, X = Cl, Me, etc, Y = anionic donor such as phenoxide, ketimide, amidinate, etc.), are known to be effective catalysts. This review introduces several selected efforts for efficient synthesis of ethylene copolymers containing cyclic olefins, biobased conjugated dienes, and disubstituted α-olefins, including the effect of cocatalysts. Moreover, here we introduce an analysis using XAS (X-ray absorption spectroscopy), which has been recognized as a powerful method providing direct information on the catalytically active species, such as coordination numbers and the distances of the coordinated atoms as well as oxidation state and the geometry of the metal centre in catalyst solution. Full article

Plastic pollution, driven by the durability and widespread use of polyolefins such as polypropylene (PP) and high-density polyethylene (HDPE), poses a formidable environmental challenge. To address this issue, we have developed an integrated multiscale framework that combines thermocatalytic experimentation, process-scale simulation, and molecular-level modeling to optimize the catalytic pyrolysis of PP and HDPE waste. Under the identified optimal conditions (300 °C, 10 wt % HMOR zeolite), liquid-oil yields of 60.8% for PP and 87.3% for HDPE were achieved, accompanied by high energy densities (44.2 MJ/kg, RON 97.5 for PP; 43.7 MJ/kg, RON 115.2 for HDPE). These values significantly surpass those typically reported for uncatalyzed pyrolysis, demonstrating the efficacy of HMOR in directing product selectivity toward valuable liquids. Above 400 °C, the process undergoes a pronounced shift toward gas generation, with gas fractions exceeding 50 wt % by 441 °C, underscoring the critical influence of temperature on product distribution. Gas-phase analysis revealed that PP-derived syngas contains primarily methane (20%) and ethylene (19.5%), whereas HDPE-derived gas features propylene (1.9%) and hydrogen (1.5%), highlighting intrinsic differences in bond-scission pathways governed by polymer architectures. Aspen Plus process simulations, calibrated against experimental data, reliably predict product distributions with deviations below 20%, offering a rapid, cost-effective tool for reactor design and scale-up. Complementary density functional theory (DFT) calculations elucidate the temperature-dependent energetics of C–C bond cleavage and radical formation, revealing that system entropy increases sharply at 500–550 °C, favoring the generation of both liquid and gaseous intermediates. By directly correlating catalyst acidity, molecular reaction mechanisms, and process-scale performance, this study fills a critical gap in plastic-waste valorization research. The resulting predictive platform enables rational design of catalysts and operating conditions for circular economy applications, paving the way for scalable, efficient recovery of fuels and chemicals from mixed polyolefin waste. Full article

Calcined and acid-leached kaolin impregnated with Fe(NO₃)₃·9H₂O (6.6 wt. % Fe₂O₃) was developed as an inexpensive bifunctional catalyst for the slow fixed-bed pyrolysis of polypropylene (PP) and low-density polyethylene (LDPE). Experiments were run with catalyst-to-plastic mass ratios of 1:4, 1:2, and 1:1 in a quartz tube reactor heated from 25 to 800 °C. For PP, increasing the Fe/kaolin loading progressively raised non-condensable gas from 26 wt. % to 44 wt. % and drove liquid aromatics from 27.9% to 72.3%, while combined paraffins olefins fell to 2.5% and wax exhibited a 46 → 24 → 36 wt. % trend. In contrast, LDPE at a 1:4 ratio already yielded 56 wt. % oil and only 22 wt. % wax; further catalyst addition mainly enhanced CH₄/CO-rich pyrolysis gas (PyGas) and char without substantially boosting aromatics. Gas analysis confirmed that Fe₂O₃ reduction and kaolin de-hydroxylation generated in situ H₂O, CO, and H₂. Given the catalyst’s low cost, regenerability, and ability to valorize the two most abundant waste polyolefins within the same reactor, the process offers a scalable route to flexible fuel and gas production from mixed plastic streams. Full article

Currently, a significant percentage of the industrial production of polyolefins and olefin-based copolymers is performed via free-radical polymerization, requiring demanding reaction conditions (i.e., high pressure and temperature) or via catalytic coordination insertion polymerization relying on the use of transition-metal catalysts. In general, these catalysts are not compatible with polar monomers, are air-sensitive and have to be used in high concentrations, which may preclude their use in specific applications. On the other hand, metal-free radical polymerization is a more robust method in terms of compatibility with air and types of monomers, with the limitation of requiring demanding reaction conditions. Nevertheless, the pursuit for strategies to synthesize olefin-based polymers under milder reaction conditions via metal-free radical polymerization is an active area in polymer science. The revision of the state of the art of such approaches is the focus of this contribution. Full article

Chemical recycling via catalytic pyrolysis is constrained by coke deposition and costly catalyst make-up. We investigate polypropylene (PP) and low-density polyethylene (LDPE) conversion over a spent FCC equilibrium catalyst (AXL) and, critically, quantify the re-activation energy landscape of the resulting coke. Using a semi-batch reactor (350 °C) and thermogravimetric analysis to 1100 °C combined with the Ozawa–Flynn–Wall method, we distinguish soft and hard coke under inert, oxidative, and sequential N₂ to air regimes. LDPE yields mainly gas (70.7 wt%) with 5.5 wt% coke, whereas PP favors liquids (47.1 wt%) with 3.4 wt% coke. LDPE-derived coke is softer (71% of total; E_A = 170 kJ mol⁻¹ soft) than PP coke (60% soft; E_A = 166 kJ mol⁻¹), evidencing a more refractory PP residue. Oxygen lowers E_A to ~155 kJ mol⁻¹ for both polymers. We introduce a simple TGA-based “softness ratio” to guide regeneration severity and show that a refinery-waste FCC catalyst delivers selective plastic-to-fuel conversion while enabling energy-aware regeneration protocols. The framework directly supports scale-up by linking polymer structure, coke quality, and atmosphere-dependent re-activation energetics. Full article

Linear Low-Density Polyethylene (LLDPE) is a versatile polyolefin made by copolymerizing ethene with minor amounts of a 1-alkene. The short side chain branches in the comonomer units partly hinder the ability of the polyethylene main chain to crystallize, thus providing a way to fine-tune material properties between the extremes of a thermoplastic and a moderate elastomer. In this function, higher 1-alkenes such as 1-hexene or 1-octene are more effective than shorter homologs like propene or 1-butene, because their alkyl substituents are fully incompatible with the polyethylene lattice. On the other hand, the former comonomers are also more expensive and, above all, poorly reactive with heterogeneous Ziegler–Natta (ZN) catalysts, the workhorses of the polyolefin industry; as a matter of fact, they can only be used with technologically more demanding molecular catalysts. The molecular kinetic factors governing this important and complicated catalytic reactivity are still poorly understood, and perusal of the literature led us to conclude that data reliability is often questionable due to experimental limitations in reaction equipment and protocols, particularly in academic laboratories. In this study, we made use of a state-of-the-art High-Throughput Experimentation workflow to measure the reactivity ratios with ethene of two representative higher 1-alkenes, namely 1-hexene and 1-decene, in the presence of a variety of well-defined molecular catalysts of metallocene and post-metallocene nature comparatively with a typical MgCl₂/TiCl₄ ZN catalyst for polyethylene application. We found that the two comonomers react almost identically with molecular catalysts, whereas a major decrease in reactivity for 1-decene compared with 1-hexene was observed idiosyncratically for the ZN catalyst. In our opinion, the overall results suggest that in the latter case, surface effects can be dominant over direct comonomer interactions with the coordination sphere of the active metal in dictating the observed molecular kinetic behavior. Full article