Cracking Activity Research Articles

Relating ten years of rock temperature monitoring to rockwall weathering processes in steep mountain valleys in western Norway

Most existing studies on rockwall frost regimes and frost weathering at rockwalls focus on permafrost-affected rockwalls. However, a high share of rockwall surface areas in Norway and in many other cold-climate environments is actually free of permafrost. It is therefore of interest how these permafrost-free rockwall systems will respond to future changes in air and rock temperatures. In this study, we report field measurements conducted at rockwalls beneath the current permafrost limit and investigate thermal regimes at rockwalls that include both rockwall areas with and without permafrost. We present a unique dataset of up to ten years of rockwall temperature measurements from ten temperatures sensors installed in two mountain valleys in western Norway. An analysis of the different rockwall thermal regimes with respect to rock weathering and associated rockfall supply for both, permafrost-affected and permafrost-free rockwalls is provided. The highest intensity of recent rockwall weathering including determined rockwall retreat rates and associated rockfall supply is detected for northeast-facing rockwalls followed by south-facing rockwalls in our study area. Frost cracking activity, probably in the form of segregation ice growth, seems to be an important factor particularly for the high weathering intensity on northeast-facing rockwalls whereas solar radiation-induced thermal stresses, which favour incremental subcritical crack growth, is assumed to play a relevant role in the moderate weathering intensity on south- and southwest-facing rockwalls. A mean annual and study area-wide rockwall retreat rate of 0.24 mm yr−1 is estimated for our ten-year investigation period (2010−2020) which is comparable to other published rates in similar lithologies and climates. As it can be assumed that seasonal frost regimes and permafrost will react differently to ongoing and future climate changes, more attention should be paid to analyse these two different thermal regimes with respect to possible varied implications for mechanical rockwall weathering and associated rockfall supply.

Investigation on the Hydrothermal Condition in Synthesis of Active Matrix from Metakaolin: Physicochemical Properties and Intrinsic Cracking Activities

The current trends in research and development of FCC catalyst is focused on the formulation of active matrices that serve as pre-crackers, with the objective of reducing the diffusional resistance of the longer chain hydrocarbon molecule in the feed. In this study, an aluminosilicate active matrix was synthesised from metakaolin using hydrothermal method. The experimental variables that were varied were hydrothermal temperature, in the range of 80 to 110 °C, and hydrothermal time, in the range of 12 to 72 hours, to investigate the best conditions for synthesising the active matrix. Subsequently, the active matrix was subjected to a series of analyses, including X-ray fluorescence, X-ray diffraction, N2 physisorption, NH3-temperature programmed desorption, Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetry, with the objective of determining its composition, crystal characteristics, surface characteristics, acidity, functional groups, material structure, and thermal characteristics. Additionally, the active matrix was tested for its intrinsic cracking activity using the micro activity test (MAT). The results indicate that the best temperature for hydrothermal synthesis of the active matrix is 80 °C. The active matrix synthesised with a heating time of 24 hours demonstrated the highest light cycle oil yield, reaching 38.9 wt%. Meanwhile, the active matrix synthesised at 48 hours exhibited the most favourable characteristics, with a specific surface area of 144.23 m2/g and a pore volume of 0.9933 cm3/g, as well as the highest cracking conversion of 70.0 wt%. Copyright © 2024 by Authors, Published by BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Electronic synergy between NiCo2O4 and adjacent carbon defects to enhance styrene cracking activity for styrene-saturated activated carbon regeneration

The design and construction of catalysts featuring abundant electron transfer and defect structures for the regeneration of styrene-saturated activated carbon (AC) pose a significant challenge. This paper presents successful preparation of a regenerated adsorbent with synergistic catalytic active sites of NiCo2O4 spinel and carbon defects using a simple impregnation method. Enhanced catalytic activity is attributed to the electronic synergy between NiCo2O4 and carbon defects in 2.5Ni-2.5Co-900, involving substantial electron transfers, abundant acidic sites, and strong reducibility. Reactive oxygen species and the robust oxygen transfer facilitate the deep oxidation of intermediates and carbon elimination. The optimized regenerated adsorbent achieved a styrene adsorption capacity of 446.4mg/g with a recovery of 92.4% of the fresh sample, which is 1.5 times higher than 5Ni-900 and about 1.8 times higher than the unmodified regenerated activated carbon sample, RAC-900. The mechanism of styrene cracking and the evolution of intermediates were investigated using thermogravimetric-infrared coupling, and the effects of catalytic temperature and active sites on styrene cracking, deep oxidation of intermediates, and elimination of carbon deposits were explored. Kinetic analysis demonstrated that the adsorption of styrene on regenerated samples entailed a multifaceted process integrating both physical and chemical adsorption. The significance of chemical adsorption became increasingly evident as the concentration of defective sites grew. Intra-pore diffusion is the main determining step of the adsorption process. After five cycles, the adsorption capacity of 2.5Ni-2.5Co-900 decreased to below 25%, suggesting promising strategies to overcome challenges of regenerating styrene-saturated AC.

Investigation of static mechanical characteristics and numerical simulation of fractal gangue cemented backfill materials

This study investigated the static mechanical responses of gangue cemented backfill materials (GCBM) with aggregate particle size distribution (APSD) satisfied fractal grading theory. The recycling of gangue in GCBM alleviates gangue accumulation pollution and improves mining production efficiency. Macroscopically, uniaxial compression experiments regarding various loading strain rates (ε̇) on gangue cemented backfill specimens (GCBS) were conducted. Acoustic emission monitoring and digital image correlation technique were employed to reveal crack activities and strain field evolution in real time. Microscopically, scanning electron microscopy and numerical specimens considering APSD were utilized to analyze the microstructure and damage process. The deterioration mechanisms and quantified number of cracks were explored at the micro level. The conclusions are as follows: (1) The axial stress (σ) of GCBM increased with fractal dimension (D) of APSD and ε̇. For the same σ, cumulative AE counts decreased with increasing ε̇ and D. (2) The main failure mode of the GCBS under static loading was tensile failure, exhibiting tensile cracks initiating at the bonding–aggregate interface. (3) The increase in the proportion of fine aggregate contributed to the optimization of the microstructures of the GCBS (4) An increased proportion of fine aggregate in the GCBS improved the synergistic load-bearing capacity between the cementing and aggregate mediums, leading to an enhancement in the σ.

Supporting the infrastructure operators with customer specific AE-monitoring solutions

Cost-effective and efficient monitoring of infrastructure is crucial for planning maintenance and repairs while ensuring the safety of the structure. Acoustic emission is a method particularly suitable for long-term monitoring. However, the necessary extended monitoring period incurs high costs for the operator, primarily due to the exceptionally high costs of measuring equipment. The need for a tailored monitoring system for infrastructure applications is evident. TÜV AUSTRIA is developing a monitoring system called RISE, which represents a customized solution for steel bridge monitoring. The innovative online monitoring solution RISE assists experts with structural monitoring. Due to its compact design, low power consumption, and easy installation, the measuring system is specifically designed for continuous monitoring. Specifically, RISE is introduced for the hotspot monitoring of railway steel bridges. The passage of trains triggers a material response that can be recorded by the measuring system. This is used to perform crack monitoring on bridges and to have a tool for assessing crack activity and the degree of damage. This enables targeted planning of repairs and maintenance activities. Reducing the operating costs of the structure and ensures it save operation. The system is being developed to function robustly and provide a high level of automation. A demonstration of AE-monitoring of active cracks on a main bridge girder was done during a fatigue test in cooperation with the TU Graz. The girder was removed from a deconstructed bridge.

Insights into Si/Al ratios for enhanced performance of β-zeolites in thermocatalytic cracking of crude oil to light olefins

The escalating demand for key petrochemicals, particularly ethylene and propylene, underscores the critical need for proficient catalysts in crude oil conversion processes. Attaining high propylene selectivity necessitates catalysts with superior adsorption capacity, thermal stability, moderate surface acidity, and pores large enough to facilitate the diffusion of larger crude oil molecules. In the present study, three different BEA Zeolites (β-zeolite) catalysts were successfully synthesized by hydrothermal method and used for catalytic cracking of Arabian Light crude oil to produce valuable petrochemical products, such as propylene, ethylene, and naphtha. The catalysts were characterized using 27Al and 29Si NMR, NH3-TPD, BET, XRD, TGA, FTIR, XRF, and FE-SEM. The thermocatalytic cracking of Arabian Light crude oil was evaluated in a fixed-bed microactivity test (MAT) unit between 550 and 600 °C. The as-prepared β-zeolite with a Si/Al ratio of 50 exhibited better catalytic activity in the catalytic cracking of Arabian Light crude oil compared to counterparts with Si/Al ratios of 35 and 65, This superiority can be attributed to its optimal combination of surface acid site distribution, textural properties, surface morphology, and high adsorption capacity. The highest feed conversion (83.4 %) and selectivity to propylene (16.11 %) were attained using β-zeolite with a Si/Al ratio of 50 at 600 °C. Importantly, our findings suggest that these catalysts hold significant potential, rivalling primary MFI catalysts like ZSM-5 commonly employed in similar reactions. This underscores their promise as catalysts of choice in the realm of catalytic cracking processes, paving the way for advancements in petrochemical production.

STUDY OF THE COMBINED EFFECT OF POST-SYNTHETIC ALKALINE TREATMENT AND NICKEL MODIFICATION OF MFI ZEOLITE ON THE DYNAMICS OF ITS DEACTIVATION IN THE PROCESS OF REFINING STRAIGHT-RUN GASOLINE

To determine the combined effect of post-synthetic treatments on the catalytic properties of MFI type zeolite (other names ZSM-5 or pentasil) during the upgrading of straight-run gasoline fraction of oil, MFI zeolite was synthesized and on its basis a sample was obtained, treated with an alkaline solution, as well as a nickel-containing sample after alkaline treatment of the zeolite. Modification of zeolite powder treated with an alkaline solution with nanosized nickel powder was carried out by dry mechanical mixing of the original powders in a vibrating mill. The activity and dynamics of deactivation of the obtained zeolite catalysts during the upgrading of straight-run gasoline fraction of oil were studied. Along with determining the characteristics of the target reaction products - high-octane gasoline, an analysis of the resulting gaseous hydrocarbons was carried out and the amount of carbon compaction products was determined. It has been shown that post-synthetic treatments of zeolite have a positive effect on the qualitative composition and yield of catalysates and reduce the rate of deactivation of zeolite catalysts. Post-synthetic alkaline treatment of MFI zeolite significantly reduces its aromatizing and cracking activity, resulting in an increased yield of high-octane gasoline with improved environmental characteristics. The introduction of nickel nanopowder into alkali-treated zeolite further enhances this tendency. Carrying out post-synthetic treatments of zeolite increases the time of stable operation of the resulting zeolite systems in the process of upgrading straight-run gasoline and reduces the amount of carbon compaction products formed. The state, location and dimensions of the zeolite carrier, nickel particles and carbon compaction products were determined using the transmission electron microscopy method. It has been shown that oxidative regeneration of a carbonized catalyst makes it possible to almost completely remove the resulting carbon deposits from the surface of both the active component and the zeolite support. For citation: Velichkina L.M., Gerasimov E.Yu., Vosmerikov A.V. Study of the combined effect of post-synthetic alkaline treatment and nickel modification of MFI zeolite on the dynamics of its deactivation in the process of refining straight-run gasoline. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 8. P. 103-112. DOI: 10.6060/ivkkt.20246708.10t.

Organosilane-assisted synthesis of EU-1 nanozeolite aggregates with improved activity in catalytic cracking of n-hexane

One-dimensional microporous zeolite, EU-1, exhibits more favorable selectivity of propylene in cracking of petroleum components. However, it faced the problem of low catalytic activity for the poor utilization of active sites. In this work, dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (TPOAC) was used to functionalize protozeolitic units and inhibit the excessive growth of crystals by the long hydrophobic alkyl chain. The introduction of TPOAC decreased the crystal sizes into nanoscale, enhanced the mesoporous volume of EU-1 zeolite, and exposed more external acid sites. Moreover, TPOAC could interact with Al species, and in this case, fewer Al atoms were incorporated into the zeolite framework, reducing the acid strength and amount. Intelligent gravitation analyzer test indicated that the zeolite prepared with the presence of 0.30 g TPOAC exhibited the largest accessible volumes in n-hexane adsorption, and the highest accessibility of acid sites, which synergistically promoted cracking of n-hexane for the production of light olefins.

Ni decorated three-dimension hierarchical pyramidal ZrO2–Al2O3 nanoporous sheets for methane production

ZrO2–Al2O3 nanocomposites were synthesized by a modified co-precipitation method and loaded with 5%Ni as catalysts for methane production via n-heptane cracking. The as-synthesized nanocomposites were characterized by several techniques such as XRD, N2 adsorption-desorption, XPS, TEM, SEM, AFM, TGA, DTG, NH3 -TPD and Raman analysis. The XRD results confirmed the synthesis of amorphous γ alumina and hexagonal phase of zirconium alumina oxide (Zr5Al3O0.5) solid solution. XRD and SEM analyses showed additional small size Related to monoclinic phase of ZrO2 particles loaded on the Al2O3 surface. BET analyses confirmed the ZrO2–Al2O3 formation in mesoporous sheets structure. TEM images of the neat alumina, 10 ZA and their corresponding Ni loaded samples (Ni@10 ZA) revealed well-defined 3D hierarchical pyramidal structures with a height about 200 nm. All catalysts under this study exhibited high tendency to favor methane production via n-heptane cracking. At higher reaction temperatures, Ni@10 ZA catalyst exhibited higher cracking activity compared to the other prepared catalysts under this investigation which confirmed by NH3 -TPD analysis. A promising yield of methane was achieved at about 88 % coupled with 94.71 % selectivity at reaction temperature of 400 °C. Herein, the data collected through this research work revealed that Ni@10 ZA is a promising candidate for methane production via n-heptane cracking.

Catalytic dehydrogenation cracking characteristics of vacuum residue over solid basic catalyst

The basic calcium aluminate with appropriate catalytic cracking activity, excellent anti-coking performance, and hydrothermal stability is of great potential for the utilization of heavy oil. However, there is a lack of systematic research on the catalytic dehydrogenation cracking characteristics of vacuum residue (VR) over solid basic catalyst. Thus, by combining the TG and Py-GC/MS methods, the dehydrogenation cracking behavior of S-VR was investigated. The results indicated that S-VR cracking on calcium aluminate leads to less coking and higher olefin content in liquid products compared with FCC catalyst and quartz sand. Then, the activation energy Ea is computed from the catalytic dehydrogenation cracking of S-VR on calcium aluminate. The results show that the Ea values from Friedman and OFW methods range from 68 to 143 kJ∙mol−1 and 114 to 192 kJ∙mol−1, respectively. After that, the molecular-level carbon number distributions of the products obtained from cracking S-VR on different reaction conditions are investigated, and the optimal reaction temperature and the heating rate are 650 °C and 1000 °C/s, respectively. Finally, the free radical regulation theory was constructed to explain the catalytic dehydrogenation cracking mechanism of basic calcium aluminate catalyst.

Assessment of Performance and Deactivation Resistance of Catalysts in the Pyrolysis of Polyethylene and Post‐Consumer Polyolefin Waste

AbstractIn the present work, the catalyst performances of USY and REY zeolites and MgO, ZnO, and MgxAlOy oxides are investigated in the pyrolysis of virgin high‐density polyethylene (HDPE) and of post‐consumer polyolefin waste. The influence of operation parameters and catalyst deactivation resistance over four reaction cycles are evaluated. The results indicate that basic oxides do not show relevant cracking activity, so that the only identified effect for these catalysts is the production of liquid products with higher contents of paraffins when compared to thermal pyrolysis. Among the evaluated oxides, MgxAlOy is the most active and resistant to deactivation. The zeolites promote cracking and secondary reactions of isomerization, cyclization, and aromatization. Particularly, USY promotes the production of higher‐quality oils and shows higher deactivation resistance, when compared to REY. Additionally, a significant loss of catalyst activity is identified in reactions conducted with post‐consumer polyolefin wastes. However, increase in rates of coke formation and the presence of contaminants (such as halogens and metals) are not detected in the catalysts after the reactions.

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.

Synthesis of ZSM-5 Zeolites from Quang Ninh Coal Ash Components and Activity for Catalytic Cracking of Low-density Polyethylene

Synthesis of ZSM-5 Zeolites from Quang Ninh Coal Ash Components and Activity for Catalytic Cracking of Low-density Polyethylene

Effect of ingredients proportions on mechanical properties in laser-coated WC-blend welds

Abstract In this study, we investigated ceramic-matrix composite coatings created by laser cladding on 45 steel using tungsten carbide (WC) powder with varying weight percentages of Co or Ni additives. Our analysis focused on the influence of Co additives in WC powders on the key properties of the coatings, including the microstructural evolution, hardness, wear, and residual stress behaviors. High residual stresses led to significant cracking in coatings comprising 100% WC. The addition of Co at a concentration of 20% to WC reduces the cracking activity. The microhardness of the coating exceeded that of the substrate by a factor of more than five. The microstructural evolution revealed a typical intergranular fracture in the molten zone, with cracks propagating through the interior of the unmelted WC at 100% WC. In addition, by adding Ni alloys, the composite coatings were extended to three mixtures: WC-Co, WC-Ni, and WC-Co-Ni. The relationship between the three-component mixtures and wear volume of the laser cladding was established, and the ratios of the three-component mixtures were optimized. A reduced quadratic model for three-component mixtures, which provided a better mixture ratio pattern, showed an excellent fit. Based on the experimental results, the developed three-component mixture with better mixture ratios can enhance anti-wear behavior. A satisfactory agreement was obtained between the predicted and experimental values of the wear volume of the laser-coated welds. Overall, our study accomplishes the optimization of the mixture ratio of the three components, which ensured a reduction in the wear of the welds, thereby improving the performance of laser-coated welds.

Regulating metal-acid double site balance on mesoporous SiO2-Al2O3 composite oxide for supercritical n-decane cracking

The balance between metal and acid sites directly affects the preparation of high-performance cracking catalysts with high heat sink and low coking. Nevertheless, how to control acid-metal sites balance and its relationship with cracking performance are reported scarcely. In this work, a series of Pt/Al2O3-SiO2 dual sites catalysts with different metal to acid active sites ratio (CM/CSA) were constructed by ethanol-assisted impregnation method and the impact on n-decane cracking under supercritical conditions was systematically and deeply investigated. The results showed that the conversion and carbon deposition increased gradually with varied CM/CSA and reached the balance at CM/CSA of 0.13. The proper ratio CM/CSA (0.13) can balance the deep dehydrogenation coking over metal active sites and high heat sink of cracking over acid active sites, the chemical heat sink reaches amazing 1.75 MJ/kg and carbon deposition is only 22.03 mg/cm2 at 750 °C. Meanwhile, the few metal sites at low CM/CSA and the few strong acid sites at high CM/CSA are the main factors limiting the cracking activity. Low CM/CSA limit the activation of C–H bond and deep dehydrogenation of coking precursor, resulting in relative low cracking activity and carbon deposition, while high CM/CSA limit the activation of C–C bond and increase the deep dehydrogenation. In this contribution, design and construction of metal-acid dual sites can not only provide the technical solution for the preparation of high heat sink and low coking cracking catalyst, but also deepen the understanding of the cracking path of hydrocarbon fuel.

Recycling waste polyethylene into fuels over Fe/USY catalyst: Evaluation on the catalytic activities of varied iron states

Iron-modified zeolite catalyst has a good application prospect on recycling the waste plastics into value-added fuels via catalytic pyrolysis. Distinguishing the catalytic activities of varied iron states on catalyst is crucial to catalyst designation and plastic-to-fuel process. In this work, we prepared three Fe/USY catalysts, termed Fe(O-550)/USY, Fe(R-300)/USY and Fe(R-450)/USY, that contain different iron states – Fe2O3, Fe3O4 + Fe (dominantly) and Fe respectively, and investigated their catalytic activities in polyethylene pyrolysis for fuel oils. The results show that loading of the iron species on USY zeolite decreases the catalyst acidity. H2 reduction treatment in catalyst preparation has no significant influence on the total acidity but slightly changes the concentration of Brønsted and Lewis acid sites. The oil yield after catalysis with different catalysts follows the order: Fe(O-550)/USY (72.5 %) > Fe(R-300)/USY (69.9 %) > Fe(R-450)/USY (66.7 %) > USY (56.5 %). The oil includes a mixture of C6-C34 compounds especially abundant in C6-C10. It is mainly in gasoline and diesel range and consists of alkanes as majority. Generally, loading of the iron species on USY zeolite increases the oil yield and produces lighter oil and more aromatics and alkenes, while the Fe(R-450)/USY shows higher catalytic cracking activity than Fe(O-550)/USY, Fe(R-300)/USY and USY catalysts. Among the varied iron states, the metallic iron is more active than the other iron oxides to promote the catalytic cracking of PE to produce fuel oil, especially the light oil and aromatic fractions.

Catalytic conversion of volatiles over homologous char: Distinct interaction patterns at different temperatures

Char produced at specific pyrolysis temperatures has specific surface properties, which is also expected to have specific interaction patterns with volatiles produced at the same temperature. In this study, the char produced at varied temperatures was used for catalyzing conversion of homogenous volatiles generated at the same temperature. The aim was to explore the change of properties of char catalyst via volatiles-char interaction, which was almost equivalent to the evolution of property of char in pyrolysis. The results suggested that the char-300 (the number refers to temperature (°C) for production of char) and char-450 retained abundant oxygen-containing functionalities, rendering them superior activity for cracking of aliphatics and aromatics, producing less bio-oil with a lower abundance of π-conjugated structures but more gases (especially over char-450, increased by 57.8%). Char-600 and char-750, with a lower abundance of oxygen-containing functionalities, were not that active for cracking or interaction with volatiles, and their properties were also not changed that much. In comparison, the spent char-300 and char-450 experienced remarkable dehydrogenation and deoxygenation via interaction with volatiles, resulting in overall net weight loss, increased carbon content as well as enhanced thermal stability, aromatic degree, and carbon crystallinity. The biggest change of char-600 and char-750 could be the filling of pores with volatiles-derived deposits. The characterization of catalytic pyrolysis with in-situ IR technique also confirmed that the char-300 showed higher capability than char-750 for catalyzing conversion –OH and CO via varied reaction routes.

Gasification of Egusi Melon (Citrullus lanatus) Shell over a Novel Ni/dolomite/MgO/[formula omitted]Al2O3 Catalyst for the Production of H2-rich gas

Hydrogen-rich gas was produced from Citrullus-lanatus in a fixed-bed reactor using a novel Ni/dolomite/MgO/γ−Al2O3 with air-steam mixture as the gasifying agent. The feed and steam-air flow rates were 3 and 0.8 kg/h with fixed steam-air volume-concentration of 40% v/v. The results displayed a high cracking activity of the hydrocarbons/tar in the biomass by the catalyst with a resultant upgrade in the gas quality/H2 yield. The highest H2 yield was 66.1 g/kg biomass, a minimal tar concentration of 2 g/Nm3 with steam-to-biomass ratio of 2 at 1100 °C. The highest H2 yield (57 vol%) was achieved at 0.28 equivalence ratio.

Preparation of hierarchical EU-1 zeolite via NH4F etching and the catalytic activity in cracking of n-hexane

One-dimensional microporous zeolite, EU-1, has tighter restriction for bulky intermediates, exhibiting more favorable selectivity of propylene than ZSM-5 in catalytic cracking. However, the diffusion limitation accelerates coke generation, passivates acid sites and deactivates the zeolite. In this study, a strategy was proposed to etch amorphous species between EU-1 nanocrystals using NH4F solution to improve the diffusion property. It was found that the etching process occurred on the crystal surface and mesopores were introduced. Catalytic performance evaluation in n-hexane cracking demonstrated that the maximum propylene selectivity over parent EU-1 was 33.6 wt% (vs. 5.7 wt% for ZSM-5). The n-hexane conversion was increased by 24 wt% over EU-1 etched in 20 wt% NH4F solution. Moreover, the introduction of mesopores provides accommodation space for coke. This study developed hierarchical EU-1 zeolite with favorable diffusion ability and reported a feasible strategy to improve the catalytic performance of EU-1 for propylene production.

Chemical upcycling of PVC-containing plastic wastes by thermal degradation and catalysis in a chlorine-rich environment

Chlorine (Cl)-containing chemicals, including hydrogen chloride, generated during thermal degradation of polyvinyl chloride (PVC) and corresponding mixture impede the chemical recycling of PVC-containing plastic wastes. While upgrading plastic-derived vapors, the presence of Cl-containing chemicals may deactivate the catalysts. Accordingly, herein, catalytic upgrading of pyrolysis vapor prepared from a mixture of PVC and polyolefins is performed using a fixed-bed reactor comprising zeolites. Among the H-forms of zeolites (namely, ZSM-5, Y, β, and chabazite) used in this study, a higher yield of gas products composed of hydrocarbons with lower carbon numbers is obtained using H-ZSM-5, thus indicating further decomposition of the pyrolysis vapor to C1–C4 hydrocarbons on it. Although the formation of aromatic compounds is better on H-ZSM-5, product distributions can be adjusted by further modifying the acidic properties via the alteration of the Si/Al molar ratio, and maximum yields of C1–C4 compounds (60.8%) and olefins (64.7%) are achieved using a Si/Al molar ratio of 50. Additionally, metal ion exchange on H-ZSM-5 is conducted, and upgrading of PVC-containing waste-derived vapor to aromatic chemicals and small hydrocarbon molecules was successfully performed using Co-substituted H-ZSM-5. It reveals that the highest yield of gas products on 1.74 wt% cobalt (Co)-substituted H-ZSM-5 is acquired via the selection of an appropriate metal and metal ion concentration adjustment. Nevertheless, introduction of excess Co into the H-ZSM-5 surface decreases the cracking activity, thereby implying that highly distributed Co is required to achieve excellent cracking activity. The addition of Co also adjusted the acid types of H-ZSM-5, and more Lewis acid sites compared to Brønsted acid sites selectively produced olefins and naphthenes over paraffins and aromatics. The proposed approach can be a feasible process to produce valuable petroleum-replacing chemicals from Cl-containing mixed plastic wastes, contributing to the closed loops for upcycling plastic wastes.