Production Of Olefins Research Articles

Catalytic mechanisms of methylcyclohexane cracking and light olefins production over zeolites

In this work, the catalytic mechanisms of methylcyclohexane (MCH) cracking and light olefins production were systematically investigated over three zeolites catalysts of Si-ZSM-5, hydrated ZSM-5 and HZSM-5. HZSM-5 exhibited the highest activity in terms of MCH conversion and selectivity towards light olefins. The mechanisms of MCH activation over HZSM-5 show that protolytic ring-opening is more energetically favorable when compared to protolytic dehydrogenation and thermal cracking. Four distinct pathways can result in the production of light olefins. But the pathway for the productions of propylene and butane is energetically favorable. Both protolytic C–C bond cleavage and the regeneration of the Brønsted acid site significantly influence production of light olefins. The rate-limiting steps for protolytic ring-opening and the production of light olefins are the initial protonation of C–C bonds. We hope this work can provide potential significance in understanding the hydrocarbon fuels cracking and aiding in identifying target products.

Hydrogenolysis of Poly(Ethylene-co-Vinyl Alcohol) and Related Polymer Blends over Ruthenium Heterogeneous Catalysts.

The hydrogenolysis of polymers is emerging as a promising approach to deconstruct plastic waste into valuable chemicals. Yet, the complexity of plastic waste, including multilayer packaging, is a significant barrier to handling realistic waste streams. Herein, we reveal fundamental insights into a new chemical route for transforming a previously unaddressed fraction of plastic waste - poly(ethylene-co-vinyl alcohol) (EVOH) and related polymer blends - into alkane products. We report that Ru/ZrO2 is active for the concurrent hydrogenolysis, hydrogenation, and hydrodeoxygenation of EVOH and its thermal degradation products into alkanes (C1-C35) and water. Detailed reaction data, product analysis, and catalyst characterization reveal that the in-situ thermal degradation of EVOH forms aromatic intermediates that are detrimental to catalytic activity. Increased hydrogen pressure promotes hydrogenation of these aromatics, preventing catalyst deactivation and improving alkane product yields. Calculated apparent rates of C-C scission reveal that the hydrogenolysis of EVOH is slower than low-density polyethylene. We apply these findings to achieve hydrogenolysis of EVOH/polyethylene blends and elucidate the sensitivity of hydrogenolysis catalysts to such blends. Overall, we demonstrate progress towards efficient catalytic processes for the hydroconversion of waste multilayer film plastic packaging into valuable products.

Kinetic analysis of monomolecular cracking of normal Alkanes (C4[sbnd]C6) over Brønsted Acid site of Zeolitic type catalyst with energetic evaluation of transition states using Quantum-Chemical modeling

The work aims to determine the kinetic parameters of reactions for production of light olefins via catalytic cracking reactions of C4–C6 n-alkanes based on the energy characteristics of the transition state using quantum chemical calculations. Cracking reactions of C4–C6 n-alkanes proceed via protolytic mechanism on the Brønsted acid sites of zeolite-containing catalysts. For kinetic studies in this work, the thermochemical parameters of the intermediate stages, including hydrocarbon adsorption and transition state were determined, then the activation energies and rate constants were determined over the temperature range of catalytic cracking process from 773 to 903 K (500–630 °C).The results showed that DFT method in combination with B3LYP and ωB97X-D functionals, and 3–21 G basis demonstrated quite high accuracy in determining thermochemical parameters, including enthalpy, entropy and Gibbs free energy at both energetic levels of adsorption and transition state. Then, modeling continued by calculations of activation energies and rate constants of reactions. Obtained kinetic parameters made it possible to determine the reactivity of hydrocarbons with different chain length. It was obtained that the rate constants of butane cracking reactions with the formation of ethylene are 54–90 times higher than the formation of propylene. The rate constants of pentane cracking reactions with the formation of butylene are on average 5 times higher than the formation of propylene. The rate constants for hexane cracking reactions with the formation of butylene are 2.9–3.7 times higher compared to the formation of propylene.

Fischer-Tropsch to olefin reaction over Fe-based catalysts: Effect of preparation method and synergistic effect of Mn and Zr promoters

BackgroundDirect production of light olefins (basic chemical raw materials in the industrials) from syngas using promoted catalysts demonstrates great potential, because of their upgraded performances. MethodsIn this study, a series of Fe-based catalysts promoted by Mn and Zr were prepared by hydrothermal and microemulsion methods and applied to the Fischer-Tropsch reaction. To optimize the catalysts, response surface methodology combined with the central composite design was applied to three independent parameters of the synthesis method, weight percent of Zr promoter (2th promoter) and reaction temperature. To clarify the relationship between the synthesis methods, the synergistic effect of Zr and Mn promoters, and catalyst performance, in detail, different characterization analyses were studied, including XRD, BET, SEM-EDS, FESEM, TEM, H2-TPR, and CO-TPR. Significant findingsAccording to developed statistical equations, it was revealed that the synthesis method is the most influential parameter on CO% and O/P ratio. The experimental results indicated that Zr and Mn promoters had a negative synergistic effect on the CO% and O/P, but a positive one on the heavy hydrocarbons selectivities. The characterization results demonstrated that hydrothermal prepared FeMn catalyst, due to having uniform particle size distribution, cubic morphology, and better reduction at low temperature had highest CO%.

Enhanced light olefin production from CO2 over potassium promoted Fe–Co bimetallic ZrO2 supported catalysts

Over 1300 tons of carbon dioxide (CO2) is emitted into the earth's atmosphere every second, threatening to breach the limiting global temperature increase of 1.5 °C set under the Paris Agreement. It is considered as sustainable feedstock that ensures season-wide availability for producing oxygenates and olefins. Likewise, CO2 hydrogenation to lower olefins was performed using bimetallic Fe-Co catalysts, processed in situ in a fixed-bed catalytic microreactor at 280–380 °C and a pressure of 0.5–3 MPa. A MOF framework (UIO-66) was used to fabricate ZrO2 NPs. In addition, a series of potassium-promoted Fe-Co bimetallic catalysts over the ZrO2 NPs were prepared, characterised and studied for the hydrogenation of carbon dioxide to light olefins. With increasing K content, the selectivity of C2-C4 increased under all operating conditions. The spent catalyst exhibits the bimodal size distribution of Fe3C, Fe2O3 and Fe° after a modified Fischer-Tropsch synthesis (M−FTS) reaction. The XANES data shows that the energy of the Fe K-edge and the Zr K-edge are shifted in a positive direction compared to the respective foil, indicating the presence of oxides in the fresh catalyst. Under the optimised reaction conditions, the H2-pretreated K promoted Fe-Co catalyst (K5Co3Fe10/ZrO2) showed remarkably low methanation with an olefin (C2-C4) selectivity of 38 %. In addition, the catalyst exhibits excellent stability and activity, providing nearly constant CO2 conversion and selectivity of (C2−C4=) lower olefins, CO and paraffin over the 100 h time-on-stream.

Synthesis of gem‑bromofluoroolefins using singlet bromofluorocarbene generated from ethyl dibromofluoroacetate via a Wittig-type reaction

A halon-free method for the synthesis of gem‑bromofluoroolefins utilizing ethyldibromofluoro-acetate is disclosed via a Wittig type reaction. The reaction system takes advantage of inexpensive and readily available reagents. The method was applied to a wide variety of aryl aldehydes. Both electron donating and electron withdrawing moieties on the aryl ring were tolerated and the desired olefin products were obtained in good to excellent yields.

Hydrodechlorination of trifluoro-trichloroethane to chlorotrifluoroethylene: Revealing the deactivation mechanism and regeneration strategy of Pd-Cu/AC catalyst

Chlorotrifluoroethylene (CTFE) is a vital fluorinated olefinic monomer produced through the catalytic hydrodechlorination of trichlorotrifluoroethane (CFC-113), an eco-friendly process. However, hydrodechlorination catalysts for olefin production often suffer from poor stability. The Pd/AC catalyst and Pd-Cu/AC catalyst prepared by co-impregnation method exhibited poor stability, Pd-Cu/AC catalyst with CFC-113 conversion dropping to around 37% after 50 h of hydrodechlorination reaction. BET, TEM, XPS and XRD of fresh and deactivated Pd /AC catalysts indicate that the deactivation of Pd /AC catalysts is due to high-temperature agglomeration of Pd. Comparative analysis of fresh and deactivated Pd-Cu/AC catalysts using BET, TEM, and TG techniques revealed decreased dispersion of active sites, reduced surface area, catalyst aggregation deactivation, and a significant decrease in Cu content. Furthermore, the results of NH3-TPD revealed that the acid sites of the catalyst increased significantly. XRD spectra indicated the formation of new species, basic copper chloride (Cu2(OH)3Cl), during the reaction. As the reaction progressed, these new species agglomerated, leading to a gradual loss of catalyst activity. Moreover, the deactivated catalyst was successfully reactivated using a simple alkaline washing method.

Production planning optimization framework for integrated refinery, ethylene and aromatics industrial chains considering environmental performance

Nonlinear modeling for the processing units and enterprise-wide optimization are essential to improve the overall profitability of production planning in the petrochemical enterprise. This study proposed a novel data-driven modeling approach for the ethylene plant and enterprise-wide production planning optimization framework for integrated the refinery, the ethylene plant and the aromatics complex considering environmental impact. The data-driven model was developed for different feedstocks in the ethylene plant to better predict product yield. The integrated model increased potential profitability of the petrochemical enterprise through considering the material balances of the intermediate products between the refinery, the ethylene plant and the aromatics complex. The integrated model planned utilization of dry gas resources, which reduced the waste of C2 and C3 resources and increased the production of olefin products. The enterprise-wide multi-period production planning model was constructed to optimize the planning operation of the refinery, the ethylene plant and the aromatics complex simultaneously, which was solved with the commercial optimization solver SBB. An industrial scenario was investigated to demonstrate the performance of the proposed model. Computational results for several cases indicated that integrated approach achieves a significant improvement in overall profit and provide valuable guidance for emission reduction.

Catalytic hydrogenolysis of polypropylene and polyethylene mixtures: Effect of temperature on liquid alkane components

This study explored the interactions between different polyolefins using a commercial Ru/C catalyst-mediated hydrogenolysis of polypropylene (PP), low-density polyethylene (LDPE), and their mixtures. The effects of the mass ratio of polyolefins to the catalyst, temperature, pressure and time on the yield of products and the internal components of liquid alkane products were studied, and the optimum conditions for solo plastic hydrogenolysis were determined. The highest liquid alkane yields of PP (46.70 %) and LDPE (70.70 %) were obtained at 250 and 210 °C, respectively. Further, the interactions between PP and LDPE during co-hydrogenolysis were observed. The temperature had a significant influence on the gaseous and liquid products, and we proposed a two-step hydrogenolysis reaction process for a mixture of polyethylene with polypropylene conducted at various temperatures. Co-hydrogenolysis provides a high-value utilization path for polyolefins that are difficult to separate during recovery.

Progress through Temporal Analysis of Products and Steady‐state Isotopic Transient Kinetic Analysis to Elucidate Oxidation, CO2 Hydrogenation and Lower Olefins Production Reactions

A prerequisite for the development or optimization of heterogenous catalysts is a comprehensive understanding of the reaction mechanism and kinetics at the level as elementary as possible. In comparison with steady‐state catalytic tests typically used for this purpose, non‐steady‐state (transient) studies provide deeper insights due to higher time resolution. For several decades, temporal analysis of products (TAP) and steady‐state isotopic transient kinetic analysis (SSITKA) have been successfully applied to the analysis of various heterogenous reactions. In this review, we highlight the contributions made by TAP and SSITKA studies between 2017 and 2023 to the understanding of reaction mechanisms and to the derivation of microkinetics. The versatility of these methods is illustrated by the examples of oxidative coupling of methane, CO/CO2 hydrogenation to hydrocarbons or methanol, metathesis of ethylene with 2‐butenes to propene, acrolein oxidation to acrylic acid, methanol conversion to olefins and non‐oxidative propane dehydrogenation to propene. We also provide our personal views on possible developments in this area.

CO Cofeeding Affects Product Distribution in CH3Cl Coupling over ZSM‐5 Zeolite: Pressure Twists the Plot

AbstractC1 coupling reactions over zeolite catalysts are central to sustainable chemical production strategies. However, questions persist regarding the involvement of CO in ketene formation, and the impact of this elusive oxygenate intermediate on reactivity patterns. Using operando photoelectron photoion coincidence spectroscopy (PEPICO), we investigate the role of CO in methyl chloride conversion to hydrocarbons (MCTH), a prospective process for methane valorization with a reaction network akin to methanol to hydrocarbons (MTH) but without oxygenate intermediates. Our findings reveal the transformative role of CO in MCTH at the low pressures, inducing ketene formation in MCTH and boosting olefin production, confirming the Koch carbonylation step in the initial stages of C1 coupling. We uncover pressure‐dependent product distributions driven by CO‐induced ketene formation, and its subsequent desorption from the zeolite surface, which is enhanced at low pressure. Inspired by the above results, extension of the co‐feeding approach to CH3OH as another simple oxygenate showcases the additional potential for improved catalyst stability in MCTH at ambient pressure.

CO Cofeeding Affects Product Distribution in CH3Cl Coupling over ZSM-5 Zeolite: Pressure Twists the Plot.

C1 coupling reactions over zeolite catalysts are central to sustainable chemical production strategies. However, questions persist regarding the involvement of CO in ketene formation, and the impact of this elusive oxygenate intermediate on reactivity patterns. Using operando photoelectron photoion coincidence spectroscopy (PEPICO), we investigate the role of CO in methyl chloride conversion to hydrocarbons (MCTH), a prospective process for methane valorization with a reaction network akin to methanol to hydrocarbons (MTH) but without oxygenate intermediates. Our findings reveal the transformative role of CO in MCTH at the low pressures, inducing ketene formation in MCTH and boosting olefin production, confirming the Koch carbonylation step in the initial stages of C1 coupling. We uncover pressure-dependent product distributions driven by CO-induced ketene formation, and its subsequent desorption from the zeolite surface, which is enhanced at low pressure. Inspired by the above results, extension of the co-feeding approach to CH3OH as another simple oxygenate showcases the additional potential for improved catalyst stability in MCTH at ambient pressure.

Combined Strategies Enable Highly Selective Light Olefins and para-Xylene Production on Single Catalyst Bed.

Achieving multiple high-value-added chemical production through novel reaction processes and shape-selective catalytic strategy is the key to realizing efficient low-carbon catalytic processes. In this work, a methanol-toluene coreaction system was developed, and combined control strategies of reaction pathway guidance and shape-selective catalysis were applied for the successful production of light olefins and para-xylene on single HZSM-5 catalyst bed. Cofeeding toluene additionally provides reactive and flowing aromatic hydrocarbon pool species that change the dominant reaction pathway in the complex network of the methanol reaction on HZSM-5 and promote the formation of ethylene. For the first time, the key reaction intermediates methylmethylenecyclodiene are directly captured and identified by experimental and theoretical techniques. This helps to propose the catalytic cycle for the dominant generation of ethylene and, more importantly, enriches the methanol-to-hydrocarbons (MTH) chemistry and hydrocarbon pool mechanism. Furthermore, 0.4HZSM-5@S-1-CLD, an optimized HZSM-5 catalyst modified by the silicalite-1 epitaxial growth followed by silanization approach, realizes highly selective production of light olefins (especially ethylene) and para-xylene, while excellent reactant activity is maintained. This highly efficient coreaction route gives an important leading significance in synthesizing the raw materials for the polyolefin and polyester industries. The establishment of the combined control strategies provides a model for the joint production of multiple target chemicals in complex catalytic processes.

Transition State Analysis of Key Steps in Dual Photoredox-Cobalt-Catalyzed Elimination of Alkyl Bromides.

A combination of inter- and intramolecular 13C kinetic isotope effects and density functional theory analysis is used to evaluate the key mechanistic events of sequentially operating catalytic cycles in the dual photoredox-cobalt-catalyzed elimination of alkyl bromides. The results point to a mechanism proceeding via irreversible halogen-atom transfer (XAT) from the alkyl halide, resulting in an alkyl radical, which undergoes hydrogen-atom transfer (HAT) to a Co(II) intermediate to deliver the product olefin. Alternative pathways involving nucleophilic substitution by a Co(I) species and by β-hydride elimination are discounted based on the poor agreement of experimental and predicted 13C KIEs. This mechanistic understanding is used to evaluate the origins of regioselectivity in the elimination step for an unsymmetrical alkyl halide catalyzed by electronically and sterically distinct cobaloxime catalysts. This study represents the experimental validation of the key features of the transition state structure of XAT by α-aminoalkyl radicals, an important class of atom transfer reactions that generate carbon-centered radicals from alkyl and aryl halides. Furthermore, it illustrates the power of 13C KIEs in probing complex mechanisms in metallaphotoredox catalysis.

Cobalt catalyzed practical hydroboration of terminal alkynes with time-dependent stereoselectivity

Stereodefined vinylboron compounds are important organic synthons. The synthesis of E−1-vinylboron compounds typically involves the addition of a B-H bond to terminal alkynes. The selective generation of the thermodynamically unfavorable Z-isomers remains challenging, necessitating improved methods. Here, such a proficient and cost-effective catalytic system is introduced, comprising a cobalt salt and a readily accessible air-stable CNC pincer ligand. This system enables the transformation of terminal alkynes, even in the presence of bulky substituents, with excellent Z-selectivity. High turnover numbers (>1,600) and turnover frequencies (>132,000 h−1) are achieved at room temperature, and the reaction can be scaled up to 30 mmol smoothly. Kinetic studies reveal a formal second-order dependence on cobalt concentration. Mechanistic investigations indicate that the alkynes exhibit a higher affinity for the catalyst than the alkene products, resulting in exceptional Z-selective performance. Furthermore, a rare time-dependent stereoselectivity is observed, allowing for quantitative conversion of Z-vinylboronate esters to the E-isomers.

Rhodium(I)-Catalyzed Defluorinative Bisarylation of Monofluorodienes with Boronic Acids.

We herein describe a Rh(I)-catalyzed bisarylation reaction of monofluorodienes using arylboronic acids. Two aryl groups are installed in the trisubstituted (E)-alkene products in one step with excellent diastereoselectivities. An intriguing reaction sequence of Rh(I)-catalyzed 1,6-addition followed by defluorinative coupling is proposed for product formation.

Enantioselective Potassium-Catalyzed Wittig Olefinations.

We report asymmetric potassium-isothiourea-boronate-catalyzed Wittig olefinations of 4-substituted cyclohexanones with non-stabilized phosphorus ylides to afford highly enantioenriched axially chiral alkenes. The optimal catalyst features an unusual macrocyclic amide-potassium-boronate chelate. Kinetic and spectroscopic analyses are consistent with a Lewis acid mechanism for the catalytic olefination that results in the formation of the oxaphosphetane adduct under cryogenic conditions. Thermal fragmentation of the oxaphosphetane to the alkene product occurs after the reaction is complete. Computational studies indicate that cycloaddition proceeds via a stepwise mechanism involving enantiodetermining polar 1,2-addition to afford an intermediate potassium betaine complex.

Improvement of catalyst activity in cracking of n-hexane via metal (Fe/Ga) impregnation over ZSM-12 catalyst

In this research, zeolite ZSM-12 with Si/Al ratio = 80 was synthesized by hydrothermal method. The synthesized zeolite ZSM-12 was modified using Fe and Ga metals and a combination of these two metals, 1 % iron metals (Z80-Fe) and 1 % gallium metals(Z80-Ga), and a 2 % combination of these two metals (Z80-Fe-Ga). The physicochemical properties of synthesized zeolites were evaluated and compared by XRD, EDX-dot-mapping, NH3-TPD, BET, FT-IR, and TGA analyses. The catalytic assessment of synthesized zeolites in the HTO (n-hexane to olefins) process in a fixed bed reactor under atmospheric pressure and Weight hourly space velocity (WHSV) equal to 4 h−1 at 550 °C was evaluated. Various parameters such as selectivity towards light olefins, propylene to ethylene (P/E ratio), production of light alkanes, and aromatic compounds (BTX) were investigated. The results show that using metals led to the improvement and adjustment of the acid sites of zeolite, and the highest amount of light olefin and the lowest amount of coke were obtained. The result of the n-hexane to olefin process showed that the yield of light olefins was significantly improved in all modified catalysts compared to parent zeolite MTW. Compared to other modified zeolites, Z80-Fe-Ga zeolite has the highest yield of light olefins, equal to 59 %. This zeolite performs better due to the presence of gallium and iron metals and shows the highest propylene selectivity (P/E = 2.4). In addition, according to the results of the TGA analysis, the content of coke on the Z80-Fe-Ga catalyst after the catalytic reaction is much less than that of other catalysts after the catalytic reactor test.

Microwave co-pyrolysis of industrial sludge and waste biomass: Product valorization and synergistic mechanisms

Microwave co-pyrolysis of textile dyeing sludge (TS) and furfural residue (FR) was investigated in this study. Comprehensive pyrolysis index (CPI) was employed to investigate pyrolysis performance and FR addition significantly improved co-pyrolysis. Product distribution showed that increasing FR ratio enhanced the bio-oil and gas with significant reduction in biochar. For bio-oil, FR addition neutralized the strong alkalinity and inhibited the formation of nitrogen compounds. Moreover, bio-oil maintained a very low oxygenates content (0.97–5.97%). For biochar, co-pyrolysis was favorable for the enrichment of C and H and mitigated the potential contamination. FR addition increased the calorific value and contributed to pore development of biochar. Online inspection displayed that co-pyrolysis drastically restrained the release of sulfur-compounds and nitrogenates in volatile, while enhanced the production of alkanes, aldehydes, and ketones. Moreover, the interaction between TS and FR was influenced by their major components. For heavy metals (HMs), Er was at low risk for most HMs and FR addition ratios of 40 and 80 wt% appeared to be more favorable. Principal component analysis (PCA) showed that FR addition changed the decomposition behavior and affected co-pyrolysis process. This study also evaluated the co-pyrolysis synergistic mechanisms of TS and FR. Overall, microwave co-pyrolysis is a novel and effective method to reduce environmental pollution and produce high-quality products, providing new insights for the low consumption and efficient utilization of industrial solid waste.

Effect of fast heating rate and alkaline catalyst on composition and characteristic of volatile products during catalytic upgrading of oil sand bitumen

The study was devoted to exploring the fundamental study on the upgrading of Buton oil sand bitumen (OSB) via fast alkaline catalytic pyrolysis based on the fluid pyrolysis technology. The effect of fast heating rate on the composition and molecular distribution of volatile products from the high-temperature fast pyrolysis of OSB was investigated by Py-GC/TOF-MS that could simulate the fast heating rate of industrial fluid pyrolysis process. The results showed that the volatile products of OSB under heating rates ranging from 10 to 1000 °C/s had the similar species composition. It was found that there were the highest relative content of low-carbon alkenes (C2-C4) and light aromatics (C6-C8) in volatile products under the 1000 °C/s, indicating that the fast heating rate favored the production of light alkenes and aromatics. Subsequently, a laboratory-scale fluidized bed apparatus was employed to further gain insight into fast alkaline catalytic pyrolysis behaviors of OSB. The investigation on the yield distribution, fractional- and molecular-level chemical characteristic of volatile products obtained from the fast alkaline catalytic upgrading of OSB over calcium aluminate was carried out with the aid of the comparison with that over Y zeolite-based FCC catalyst and silica sand. The results revealed that three-phase products over calcium aluminate possessed the larger selectivity of C2−C4 alkenes, larger yield of light oil and the lower coke output, which were 51.88%, 45.49% and 7.96%, respectively. On basis of the chemical structure analysis of liquid products, the alkaline catalytic upgrading of OSB over calcium aluminate could heighten the content of chain alkyl structures as well as alkyl-substituents attached to aromatic ring in liquid products. This indicated that the fast heating rate and alkaline catalyst that adopted in catalytic upgrading process of OSB could play an energetic role in optimizing the composition of volatile products. The alkaline catalytic upgrading of OSB based on fluid pyrolysis technology with the fast heating rate could heighten the yield of low-carbon olefins and light oil and lessen coke yield, meanwhile modify the chemical structure characteristics of liquid products that were conducive to the generation of valuable chemicals (light alkanes and BTX) during secondary processing of liquid products.