Propylene Yield Research Articles

Fluoride- and OSDA-free synthesis of ZSM-5 with controllable b-axis orientation: Insights into the role of medium alkalinity and seed induction

MFI-topology nanosheets with a b-axis-oriented structure are valuable catalysts in diffusion-controlled acid-catalyzed reactions. Therefore, b-axis-oriented ZSM-5 nanosheets were synthesized herein in a fluoride-free solution without using special additives and complex methods. The initial gel pH of mixed raw materials was adjusted to approximately 5–7 (weak acidity) to direct nanosheet structure formation. The target ZSM-5 zeolite with a b-axis-oriented structure was achieved through the synergistic effect between the involved gel pH and seed solution. The seed solution directed the formation of an MFI structure, and the low alkalinity of the gel limited crystal growth in the b plane, thereby affording b-axis-oriented thin sheets. The ratio of the lengths of the c and b axes of the obtained ZSM-5 could be effectively tuned by adjusting the pH of the initial gel. Compared with the nanosized hexagonal ZSM-5 sample synthesized in a strong-basic system, the as-synthesized b-axis-oriented ZSM-5 exhibited a lower coking rate and higher propylene yield during the considered 1-hexene cracking reaction.

Support induced effects on the activity and stability of Ga2O3 based catalysts for the CO2-assisted oxidative dehydrogenation of propane

The influence of the support nature (Al2O3, TiO2, SiO2) on the activity and stability of supported Ga2O3 (10 wt%) catalysts was investigated for the production of propylene through the CO2-assisted oxidative dehydrogenation of propane (CO2-ODP). Catalytic activity was found to be higher when gallium oxide was dispersed on alumina support which was characterized by the highest acid site density and moderate surface basicity. Below 650 °C propylene yield increased in the order Ga2O3-TiO2<Ga2O3-SiO2<Ga2O3-Al2O3, which was modified as Ga2O3-Al2O3<Ga2O3-TiO2<Ga2O3-SiO2 for higher reaction temperatures. Propylene selectivity decreased with increasing reaction temperature followed by an increase of ethylene and methane selectivity implying that the side reactions of propane hydrogenolysis and propane/propylene decomposition were facilitated at higher temperatures hindering the CO2-ODP reaction. Gallium oxide catalysts supported on TiO2 and SiO2 exhibited sufficient stability for 30-35 hours on stream at 660 and 710 οC, contrary to Ga2O3-Al2O3 which although was stable at 710 οC it was gradually deactivated when the reaction was taking place at 600 °C. Temperature programmed oxidation experiments showed that carbon deposition was favored over Ga2O3-Al2O3 catalyst when the reaction was conducted at low temperature, which may be related to the higher surface acidity of this sample and be responsible for its deactivation with time. SEM images and elemental mapping obtained from both the freshly prepared and used Ga2O3-MxOy samples showed that Ga and M (M: Si, Ti, Al) were uniformly present even after prolonged catalyst interaction with the reaction mixture. EDS analysis indicated that carbon formation was accelerated with increasing reaction temperature.

Study on the Acidic Modification of Mesoporous HZSM-5 Zeolite and Its Catalytic Cracking Performance

Mesoporous HZSM-5 zeolites with nanocrystal stacking morphology were directly synthesized via hydrothermal methods without mesoporous templates. The synthesized mesoporous HZSM-5 was subjected to hydrothermal–citric acid washing treatment. The structural and acidic properties of the samples before and after modification were characterized using various techniques. The catalytic performance for butene conversion to propylene was investigated under atmospheric pressure, 500 °C, and a butene weight hourly space velocity (WHSV) of 10 h−1 in a continuous-flow micro-fixed bed reactor. The results show that propylene selectivity increased significantly from 24.7% before modification to 44%, and propylene yield increased from 22% to 38%. After 2 h of hydrothermal–citric acid washing modification, the catalyst maintained a butene conversion rate of 76% and a selectivity of 47% at 525 °C and a WHSV of 10 h−1 after 130 h of continuous reaction, with a propylene yield of 37%. The results indicate that moderate hydrothermal–citric acid washing modification leads to the removal of aluminum from the zeolite framework, reducing the amount and strength of acid but increasing the mesopore quantity. This helps control the reaction pathways and diffusion of intermediate products, suppresses some side reactions, and improves the selectivity and yield of the desired product, propylene, while significantly enhancing catalytic stability.

Optimizing propylene production via acetone hydrodeoxygenation: Insights from catalytic studies with Cu/γ-Al2O3 and Hβ zeolite

Propylene is a crucial light olefin in the petrochemical industry and can be produced via acetone hydrodeoxygenation, which involves two sequential reactions: first, acetone undergoes hydrogenation catalyzed by metallic sites, followed by the dehydration of the resulting isopropanol catalyzed by acidic sites. In this study, propylene production through acetone hydrodeoxygenation was investigated using a physical mixture of 35 wt% Cu/γ-Al2O3 and Hβ zeolite to investigate how various reaction parameters affect acetone conversion and propylene yield. Using the experimental design methodology, empirical models were developed to correlate acetone conversion (Xacet) and propylene yield (Yprop) with the ratio of 35 wt% Cu/γ-Al2O3 to Hβ (CR), total catalyst weight (Cw), hydrogen volumetric flow rate (FH2) and reaction temperature (T). The maximum propylene yield achieved in the catalytic tests was 73.46 %. A long-term test demonstrated the catalyst's reusability, remaining active even after 22 hours of reaction with only a slight decrease in propylene yield. Analysis of the experimental data revealed that increasing T and Cw positively affected propylene yield, whereas higher CR and FH2 had negative effects. According to the Pareto chart, reaction temperature was the most influential variable for propylene yield, followed by CR, FH2 and Cw. For acetone conversion, the order of significance among the variables was T >CR >Cw >FH2.

Enhancing catalytic pyrolysis of polypropylene using mesopore-modified HZSM-5 catalysts: insights and strategies for improved performance

Designing an active, selective, and stable catalyst for catalytic polyolefin pyrolysis is crucial for enhancing energy efficiency and economic viability in chemical processes. In this study, two synthesis methods—NaOH and NaOH/CTAB treatments—were employed to modify the physicochemical properties of CBV23, CBV55, and CBV80 zeolites. The catalytic performance of both parent and modified zeolites was evaluated for polypropylene pyrolysis using a two-stage micro-pyrolyzer coupled with two-dimensional GC-FID/MS. The NaOH/CTAB treatment preserved and enhanced strong acid sites while promoting a more uniform mesopore distribution. Among the catalysts tested, the hierarchical CBV80-ZM exhibited the best performance, achieving a propylene yield of 41 wt% and total light olefin and MA yields of 92 wt%. The improved catalytic performance was attributed to optimized acidity and larger pore size, which reduced the number of weak acid sites. These findings offer valuable insights for designing tailored zeolites based on specific target products for catalytic pyrolysis of plastic waste, particularly in the production of propylene and other high-value chemicals.

Thermal degradation of waste medical masks to light olefins in a two-stage process

The treatment of waste plastics is currently one of the most urgent environmental issues, and disposable medical masks (DMMs) are becoming increasingly important in the recycling of waste plastics. This study employs thermogravimetric analysis (TGA) combined with infrared spectroscopy (IR) and mass spectrometry (MS), and pyrolysis/gas chromatography/mass spectrometry (PyGC-MS) to investigate the thermal degradation of DMMs, including pyrolysis characteristics, kinetics, and products distribution. DMMs are composed of five layers, i.e., layers 1, 2 and 3 are the mask body, layer 4 is the mask strap, and layer 5 is the nose clip. Except layer 4, all the other layers could be entirely decomposed at 500 °C and have similar pyrolysis properties to PP. Alkanes, olefins, and diolefins with a wide carbon number distribution are produced at low temperature, while light olefins are more likely to be generated at high temperature. Accordingly, a two-stage pyrolysis reactor is applied to decompose DMMs to valuable products. After optimizing the operating conditions, the yield of light olefins reaches a maximum of 70.4 wt% at 800 °C in the second-stage pyrolysis of DMMs, where the yields of ethylene, propylene, and butene are 12.0 wt%, 28.0 wt%, and 29.6 wt%, respectively.

Optimization of ethylene and propylene yields from n-hexane catalytic cracking over H-ZSM-5 catalyst using model based design of experiments (DOE)

Catalytic cracking of n-paraffins of varied carbon chain length (C6-C11) to represent light naphtha and gasoline was studied using extrudates of H-ZSM-5 (zeolite: binder = 70: 30) as a catalyst in a fixed bed reactor. Optimization of ethylene and propylene yields using model-based design of experiments (DOE) was carried out for n-hexane cracking by varying the temperature (550–650℃), weight hourly space velocity (3.3–9.9 h−1) and carrier gas (N2) flowrates (3–10 L/h). These variables showed significant effect on the conversion of n-hexane and yield of ethylene and propylene under studied reaction conditions. The Box-Behnken design coupled with response surface methodology was used to determine the effect of reaction temperature, WHSV and N2 flow rate on the yield of ethylene and propylene. Empirical models were constructed for the response variables namely n-hexane conversion, ethylene (E) yield, propylene (P) yield and total ethylene and propylene (E+P) yield. Main effect plot showed that the average yield of ethylene and propylene increased with increase in reaction temperature and decreased with increase in WHSV. The optimization study of multiple responses showed maximum 94.7% conversion of n-hexane and 46.1 wt% yield of ethylene and propylene at 650℃ catalyst bed temperature, 3.3 h−1 WHSV and 8.3 L/h N2 flow rate. The model predicted ethylene and propylene yields matched closely with experimental data for catalytic cracking of naphtha feed at 550 and 650℃ cracking temperature.

A low-temperature regenerable catalyst for stable and selective propylene production from ethylene using Ni and P-supported SSZ-13 zeolite

Due to the increasing demand for propylene, highly selective propylene production from ethylene using small pore zeolite has received significant attention. However, rapid catalyst deactivation due to coke deposition on the catalyst impedes effective propylene production in industry. Therefore, it is essential to develop a low-temperature regeneration ethylene-to-propylene (ETP) catalyst with stable catalytic activity. To achieve such a catalyst, various hydrocracking metal species and phosphorus-supported SSZ-13 were prepared and evaluated using a one-pass ETP and ETP-Regen test. The optimized catalyst NiO(1.0)-P(0.6)-SSZ-13 exhibited a constant, excellent propylene yield of over 70 wt% with 90 wt% of propylene selectivity over ETP reaction and consecutive ETP-Regen cycles. The unprecedented catalytic performance of NiO(1.0)-P(0.6)-SSZ-13 was ascribed to the synergistic effect of NiO and P components, where nickel is responsible for catalyst recovery through effective coke removal, while phosphorus plays an essential role in size-selective diffusion.

Kinetic modeling of the effect of the conditions of conjugate oxidation of propane and ethylene on the yield of propylene

The study of the oxidation of propane-ethylene mixtures by numerical kinetic modeling allowed us to establish that in the range of 400–600 oC with an increase in the conversion of propane with an increase in temperature, the selectivity of propylene formation passes through a maximum, the position of which depends on the concentration of ethylene in the initial mixture. The addition of ethylene to the initial mixture leads to a reduction in propane consumption and an increase in the selectivity of propylene formation. The conditions under which ethylene introduced into the initial mixture is not consumed during the process are determined, so formally it can be considered as a catalyst, and the process of propane oxidation as proceeding in a pseudo-catalytic regime.

Ga2O3/La2O3-γAl2O3 catalysts for CO2-assisted propane oxidative dehydrogenation to propylene

Novel Ga2O3/La2O3-γAl2O3 was investigated for ODH of propane to propylene using CO2 as a mild oxidant in a batch scale fluidized CREC Riser Simulator. La2O3 in the catalysts provided a control of both the reducibility and acidity, as shown by H2-TPR and NH3-TPD, respectively. The propane conversion and products selectivity were strong function of La2O3 content in the Ga2O3/La2O3-γAl2O3 catalysts. With increasing La2O3 content in the catalyst, propane conversion dropped slightly but the propylene selectivity and yields increased. It was proposed that the presence of La2O3 reduced the non-selective sites and the acidity of the catalysts, that contributed towards deep oxidation of propane and propylene. The improved activity and selectivity with CO2 addition implied that the as-synthesized catalyst possesses CO2 activation capability required for ODH reactions. Among the investigated catalysts, Ga2O3/La2O3-γAl2O3(1:1) exhibited the highest propane conversion (92 %) and propylene yield (56 %) at 600 ℃ in the presence of CO2.

Propane dehydrogenation catalysis of group IIIB and IVB metal hydrides.

Catalytic propane dehydrogenation (PDH) has mainly been studied using metal- and metal oxide-based catalysts. Studies on dehydrogenation catalysis by metal hydrides, however, have rarely been reported. In this study, PDH reactions using group IIIB and IVB metal hydride catalysts were investigated under relatively low-temperature conditions of 450 °C. Lanthanum hydride exhibited the lowest activation energy for dehydrogenation and the highest propylene yield. Based on kinetics studies, a comparison between the reported calculation results and isotope experiments, the hydrogen vacancies of metal hydrides were involved in low-temperature PDH reactions.

Steam catalytic cracking of vacuum gas oil: Effect of co-feeding naphtha or gas condensate on light olefins yield

Herein, we have investigated the steam catalytic cracking of heavy VGO (HVGO) blends with naphtha (NAPH) and gas condensates (GCON) in a microflow fixed-bed reactor using synthesized nano-ZSM-5 catalyst for increased light olefins yield. The co-feeding of HVGO with NAPH in the steam cracking reaction increased HVGO conversion from 38.2 % to 65.3 %, and slightly decreased the coke yield. Ethylene and propylene yield increased from 10.2 % and 9. 8 % in HVGO to 15.0 % and 13.4 % in the HVGO+20 %NAPH respectively. The co-feeding of HVGO with GCON in the steam cracking reaction increased HVGO conversion from 38.2 % to 47.5 %, however, lower yield of light olefins was recorded. The catalytic cracking of HVGO with NAPH over synthesized nano-ZSM-5 zeolite resulted in higher conversion and light olefins yield. This has been ascribed to the available acid sites and shape selectivity of the nano-zeolite that favors high yield of light olefins. The HVGO+20 %GCON conversion increased to 68.6 % during catalytic cracking over nano-ZSM-5 zeolite, and the light olefins increased from 33.2 % to 41.1 %. The effect of steam/oil ratio on the catalytic cracking reactions of HVGO+20 %NAPH and HVGO+20 %GCON for steam/oil ratio 0–2 showed that higher conversion and light olefins yield were achieved at the steam/oil ratio of 2.

Kinetic modeling of the oxidative dehydrogenation of propane with CO2 over a CrOx/SiO2 catalyst and assessment of CO2 utilization

Oxidative dehydrogenation of propane with carbon dioxide (ODPC) has gained attention as a sustainable process capable of simultaneously producing propylene and reducing carbon dioxide (CO2) emissions. In this study, we developed a kinetic model of the ODPC over a silica-supported chromium oxide catalyst based on the Mars–van Krevelen (MvK) mechanism using the experimental data obtained under controlled conditions. The constructed model estimated both reactant conversions and propylene yield within an absolute error of 3% of the experimental data, confirming the integrity of the kinetic model. The kinetic analysis provides insight into the activation of propane and CO2 via several reactions occurring under ODPC conditions, emphasizing that the ODPC cycle is limited by the high energy barrier for CO2 activation. In addition, it allows comparison of the contributions of non-oxidative and oxidative dehydrogenation reactions, the two main reactions producing propylene under ODPC conditions. The estimation results show a significant increase in the reaction rate of ODPC with increasing CO2 partial pressure, in contrast to a nearly constant reaction rate of non-oxidative dehydrogenation, highlighting the promoting effect of CO2 in enhancing the ODPC reaction. Furthermore, the potential of the ODPC process is assessed by considering propylene productivity, net CO2 emissions, including the energy consumption for the separation process, and the global warming index of the energy grid. A comprehensive investigation of the ODPC process through controlled experiments, kinetic modeling and evaluation of net CO2 utilization provides insight into future strategies for using the ODPC as an efficient and eco-friendly process.

Modulating Electron Density of Boron-Oxygen Groups in Borate via Metal Electronegativity for Propane Oxidative Dehydrogenation.

The robust electronegativity of the [BO3]3- structure enables the extraction of electrons from adjacent metals, offering a strategy for modulating oxygen activation in propane oxidative dehydrogenation. Metals (Ni 1.91, Al 1.5, and Ca 1.0) with varying electronegativities were employed to engineer borate catalysts. Metals in borate lacked intrinsic catalytic activity for propane conversion; instead, they modulated [BO3]3- group reactivity through adjustments in electron density. Moderate metal electronegativity favored propane oxidative dehydrogenation to propylene, whereas excessively low electronegativity led to propane overoxidation to carbon dioxide. Aluminum, with moderate electronegativity, demonstrated optimal performance. Catalyst AlBOx-1000 achieved a propane conversion of 47.5%, with the highest propylene yield of 30.89% at 550 °C, and a total olefin yield of 51.51% with a 58.92% propane conversion at 575 °C. Furthermore, the stable borate structure prevents boron element loss in harsh conditions and holds promise for industrial-scale catalysis.

Effect of different ligands on the preparation of Pt-xMn@HZSM-5 and their catalytic performance for iso-butane catalytic cracking

ZSM-5 has emerged as a promising catalyst for iso-butane catalytic cracking due to its unique pore structures and abundant acid sites. And the optimization of catalytic performance has attracted more and more attention. Herein, a series of Pt and Mn-embedded Pt-xMn@HZSM-5 catalysts with different Mn complexes were successfully synthesized via the one-pot hydrothermal method (x refers to the Mn/Pt ratio). The ligand effects of both ethylenediamine and ethylenediaminetetraacetic acid disodium salt on the nature of target samples in terms of crystallinity, porosity, morphology, metal state, and acidity, were investigated in detail. It has been demonstrated that ethylenediamine served as a ligand enabled Pt-xMn@HZSM-5 more metal nanoparticles and acid sites, thereby delivering improved catalytic performance and high yields of ethylene, propylene and BTX (benzene, toluene, and xylene) for iso-butane catalytic cracking.

Improved dragonfly optimization algorithm based on quantum behavior for multi-objective optimization of ethylene cracking furnace

Ethylene is one of the important basic raw materials for the modern chemical production, accounting for over 75 % of petrochemical products. And the ethylene cracking furnace is subject to coking problems that can impede the thermal conductivity of the reaction tube. Therefore, an improved multi-objective dragonfly optimization algorithm based on quantum behavior is proposed. The particle evolutionary model introduces the quantum bound state δ-potential well model, which improves the global convergence ability and the convergence speed of the dragonfly optimization algorithm. In addition, the calculation formulas for parameters are improved by introducing natural logarithm and the iterative search method is changed to a triple search. Moreover, the global convergence and local search ability of the quantum behavior enhancement algorithm is assisted by adaptively selecting the search strategy according to the current number of iterations of the improved dragonfly algorithm. Compared with other multi-objective optimization algorithms on the ZDT and CEC test functions, the proposed algorithm has good global convergence and local search capabilities in terms of the inverted general distance. Finally, the proposed algorithm is applied in the multi-objective optimization of an ethylene cracking furnace, with the ethylene yield and the propylene yield as optimization objectives. The experimental results show that the ethylene yield can be increased by 1.5498 %, while the propylene yield decreases by only 0.0081 %, which proves that the proposed algorithm achieves better effect in optimizing the main product yield under fixed cycle adjustment operating conditions compared to original operating conditions.

Photothermal catalytic CO2 oxidative dehydrogenation of propane over a dual functional Pt-GaN/SrTiO3 catalyst

Photothermal CO2 oxidative dehydrogenation of propane (CO2-ODHP) is an environmentally friendly and sustainable route for propylene production and CO2 utilization. In the present work, we developed a Pt-GaN/SrTiO3 dual-functional catalyst to facilitate the reaction. The catalyst achieved propylene and CO yields of 1 mmol·gcat-1·h-1 and 1.2 mmol·gcat-1·h-1 under photothermal conditions at 320 °C, surpassing the performance of previously reported catalysts. Additionally, control experiments and in situ DRIFTS analyses corroborated that GaN and Pt were primarily responsible for the activation of C-H and CO bonds, respectively, and the photothermal route worked via a distinguished intermediate for CO2 activation in contrast to the thermal route. DFT calculations supported the reaction route involving the coupling direct dehydrogenation of propane and reverse water-gas shift reaction. The present work shines a light on the design of photothermal catalysts with dual functions, particularly for the activation of CO2 and light hydrocarbons. Additionally, it proposes a strategy to initiate high-temperature reactions at relatively lower temperatures.

Synthesis of hierarchical Fe-incorporated ZSM-5 molecular sieves with an Fe-based metal-organic framework as a mesoporogen and iron source for catalytic pyrolysis of alkanes

To increase the yield of light olefins during the catalytic pyrolysis of alkanes, a novel hierarchical Fe-incorporated ZSM-5 molecular sieve (FeM-Z5) was synthesized using an Fe-based metal-organic framework (Fe-MOF) as a mesoporogen and iron source through the dry gel conversion (DGC) method. In contrast to the conventional method of incorporating Fe species into ZSM-5 via impregnation, the DGC method incorporates Fe species into the framework of ZSM-5, decreasing the amount of Brønsted (B) acid sites and thereby inhibiting the side reactions of hydrogen transfer during the catalytic pyrolysis of alkanes. Compared with the FeN-Z5 catalyst prepared by the DGC method with Fe(NO3)3 as an iron source, FeM-Z5 had a larger amount of strong B acid sites and more mesopores with a size range of 10–40 nm originating from the decomposition of Fe-MOF; these aspects improved n-pentane pyrolysis and ethylene and propylene diffusion. As a result, the optimal FeM-Z5 catalyst exhibited the highest yield of ethylene and propylene (33.4 wt%) and the lowest deactivation rate (0.07 %/h) among the prepared catalysts during the catalytic pyrolysis of n-pentane.

Spatial-temporal self-attention network based on bayesian optimization for light olefins yields prediction in methanol-to-olefins process

Methanol-to-olefins (MTO), as an alternative pathway for the synthesis of light olefins (ethylene and propylene), has gained extensive attention. Accurate prediction of light olefins yields can effectively facilitate process monitoring and optimization, as they are significant economic indexes and stable operation indicators of the industrial MTO process. However, the nonlinearity and dynamic interactions among process variables pose challenges for the prediction using traditional statistical methods. Additionally, physical-based methods relying on first-principle theory are always limited by an insufficient understanding of reaction mechanisms. In contrast, data-driven methods offer a viable solution for the prediction based solely on process data without requiring extensive process knowledge. Therefore, in this work, a data-driven approach that integrates spatial and temporal self-attention modules is proposed to capture complex interactions. Furthermore, Bayesian optimization is employed to determine the optimum hyperparameters and enhance the accuracy of the model. Studies on an actual MTO process demonstrate the superior prediction performance of the proposed model compared to baseline models. Specifically, 24 process variables are selected as the high-dimensional inputs, and yields of ethylene and propylene, as the low-dimensional outputs, are successfully predicted at various prediction horizons ranging from 2 to 8 h.

Synthesis of hierarchical ZSM-11 and its catalytic performances during methanol to propylene

To solve the easy deactivation of zeolite catalyst in methanol to propylene (MTP) reaction, hierarchical ZSM-11 zeolite composed of loosely aggregating ultra-small nanocrystals (∼10 nm) were prepared using vinyltrimethoxysilane-methyl methacrylate (VTMS-MMA) copolymer latex as a “bond blocker”. The structure and texture properties of the as-synthesized zeolite were systematically characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption desorption, NH3-TPD, and thermogravimetric analysis (TG). The results showed that as compared with the parent ZSM-11-0 without adding the latex, the hierarchically porous ZSM-11-x (1 ≤ x ≤ 3) zeolite synthesized with VTMS-MMA copolymer latex had a higher surface area, mesopore volume, and moderate acidity. Due to the nanocrystallization of the primary grain in the polycrystalline aggregates, the micropores channels in the as-synthesized ZSM-11-x (1 ≤ x ≤ 3) were effectively shortened and abundant intercrystalline mesopores resulted from loosely aggregating of the ultrasmall primary crystals were therefore introduced, which offered the optimized ZSM-11-1 catalysts with a longer catalyst life (46 h) and a higher propylene yield (∼40.5 %) in MTP.