Oxidative Cracking Research Articles

Influence of Alloying Elements on Cyclic Oxidation Behavior of (Cu/Al) Alloys

This study is conducted to extend the effective life of Cu/Al alloy. The used samples were (Cu/9.5%Al),(Cu/9.5%Al/5%Ni),(Cu/9.5%Al/5%Ni/0.9%Mn),(Cu/%9.5Al/5%Ni/4.5%Fe), (Cu/9.5%Al/5%Ni/0.9%Mn/4.5%Fe),(Cu/9.5%Al/5%Ni/0.9%Mn/4.5%Fe/0,1%Y),(Cu/9.5%Al/5% Ni/0.9%Mn/4.5%Fe/0.2%Ge) by using powder metallurgy these samples were prepared, the cyclic oxidation test was conducted in the presence of air in a programmable furnace (typeVBF-1200X-H8-USA) at 250°C and 800°C for 50 hours at 5-hours cycle. It was represented by the weight-gain of all examined samples that the oxidation rate increased as the temperature increased. It appears that cracking or spalling of oxides was at high temperatures such it found the weight gain of the base alloy (Cu/9.5%Al) was (12.09*10−3g/cm2)at 250°C otherwise, it was (5.98*10−2 g/cm2) at 800°C for the same alloy. This is attributable to the expected behavior of oxides when stressed. The addition of Ni, Mn, & Fe to (Cu/9.5%Al) caused a relative increase in resistance to cyclic oxidation, while the addition 0.1% Y to (Cu/9.5%Al/5%Ni/0.9Mn/4.5%Fe) caused the lowest oxidation rate as compared with other alloys, it showed that the reduction in weight gain (165.13%) relative to(Cu/9.5%Al) the highest weight gain at 250°C, and it was (285.22%) relative to (Cu/9.5%Al/5%Ni) which has highest weight gain at 800 °C. Both alloying elements Y and Ge represented a major change in cyclic oxidation resistance.

Friction stir welding with weaving arrangement

Structural materials such as copper and aluminium, with comprehensive properties such as excellent thermal and electrical conductivity, are used in engineering applications. Despite the beneficial actions of aluminium and copper as a composite structure, the development of such dissimilar combinations is more difficult. Some unsolvable problems such as oxidation, tunnels, and fragmentary cracks include the fusion of dissimilar metals or alloys in the joining of Cu and Al alloys using classical methods such as fusion welding and pressure welding. The Friction Stir Welding (FSW) process has been found to be an effective method for joining different metals/alloys in solid-state joining technology to solve these problems. A non-consumable stirring tool is plunged into the base metal joints comprising a profiled pin and shoulder and is made to move in a predefined direction to stir up the bondage between the base metals. A proper stirring of base metals was achieved by tool pin eccentricity in this current investigation.

Zeolite-assisted core-shell redox catalysts for efficient light olefin production via cyclohexane redox oxidative cracking

This study reports a highly effective redox catalyst platform, i.e. composites of metal-exchanged ZSM5 and CaMn0.75Fe0.25O3@Na2WO4, for “low temperature” (<650 °C) redox oxidative cracking (ROC) of naphtha using a cyclohexane model compound. TEM-EDX showed that Na2WO4 shell covers the CaMn0.75Fe0.25O3 bulk and the zeolite + CaMn0.75Fe0.25O3@Na2WO4 composite can achieve autothermal conversion of cyclohexane under a cyclic redox scheme by selective oxidation of by-product H2 to H2O. Meanwhile, NH3-TPD and pyridine FTIR experiments confirmed that the Brönsted acidity of ZSM5 was primarily responsible for cyclohexane activation. Compared to each catalyst component alone, the synergistic effect of the composite redox catalysts resulted in substantially higher olefin yield (up to 75%), lower alkane yield (~5%), lower aromatic yield (~10%), and higher lattice oxygen utilization (up to 4 wt.cat%). Based on TGA-DSC experiments and ASPEN Plus analysis, the multi-functional redox catalysts facilitate autothermal conversion of cyclohexane with high lattice oxygen utilization from the redox catalysts. Due to the highly effective redox catalysts performance and the ease for heat integration, the novel ROC process has the potential for more energy-efficient light olefins production with significantly reduced CO2 emissions when compared to naphtha steam cracking.

Cleaner technology for the production of linear long chain α-olefins through a “millisecond” oxidative cracking process

The oxidative cracking of n-decane was investigated at millisecond contact times over platinum alumina washcoated monoliths at a fuel-air equivalent ratio (Φ) of 5. High valuable linear α-olefins were so produced through an autothermal way concomitantly with oxygenated compounds, CO, CO2, H2 and H2O.A fine identification of reaction products coupled with the study of thermal phenomena occurring with both active and deactivated catalysts allowed to investigate the n-decane transformation mechanism and to discriminate heterogeneous and homogeneous reactions. This process is a 2-zone reaction system involving catalytic combustion of one part of reactant which provides enough heat for gas phase radical transformations initiation. Long chain hydrocarbons result from homogeneous decomposition of oxygenated intermediates such as decylperoxy radicals into aldehydes and α-olefins.

Effect of Mixed Oxide Cracking Catalyst on Conversion of the Mixture of Vacuum Gas Oil and Vegetable Oil

A number of cracking catalyst samples containing Me–Mg–Al mixed oxides have been prepared. Cobalt, zinc, copper, and cerium were used as additional metals in the mixed oxide composition. When studying the cracking of a vacuum gas oil–sunflower oil mixture, catalysts containing Co–Mg–Al or Zn–Mg–Al mixed oxides were found to increase both the conversion rate of the mixed feedstock by 5.0 wt % compared to a sample containing the mixed oxide free of additional metal, and the gasoline yield by 1.6–3.0 wt %. It was discovered that the modification of mixed oxides with cobalt or zinc cations has no significant effect on the distribution of inorganic products, thereby indicating sustained catalytic activity during the decarboxylation reaction. The catalytic tests also demonstrated that catalyst samples containing mixed Mg–Al oxides with copper cations exhibited enhanced decarbonylation effect, as well as low conversion rates of the mixed feedstock and low gasoline yield, which is probably associated with the poisoning impact of copper oxide on Y zeolite.

Studying the regularities of oxidative catalytic cracking of vacuum distillates

Improving the efficiency of processing heavy oil residues into light petroleum products and raw materials is an urgent task for Kazakhstan and other countries that produce and consume petroleum products. Really the share of heavy oil and natural bitumen in the balance of hydrocarbon raw materials produced will continuously increase. The aim of the study was preparation of catalysts based on Taizhuzgen zeolite and Narynkol clay (Kazakhstan) and determination their efficiency in the process of oxidative cracking of vacuum distillates of Atyrau and Zhetybai oil. The IR spectra of the obtained gasolines indicate that the reactions of incomplete oxidation of hydrocarbons in the course of oxidative cracking practically do not occur. At low volume feed rates of the initial substance to the reactor, the yield of diene and cyclodiene hydrocarbons in the presence of air additives significantly increases in comparison with cracking carried out without air additives to the reactor. The direction of the oxidative cracking process changes with an increase in the volume rate of the suspension feed. Obviously that the air of definite concentrations in the reactor contribute to a deeper destruction of the hydrocarbons of the vacuum gas oils investigated.

Thermochemical interaction of wood and polyethylene during co-oxidation in the conditions of thermogravimetric analysis

In this work, using the methods of thermal analysis, we investigated the features of the oxidative decomposition of mixtures of polyethylene and sawdust (in different mass ratios). The results show that during the mixtures decomposition, the effects of interaction between wood and polyethylene are observed, which, apparently, are associated with the chain nature of the oxidation reactions of both components. It was found that the oxidation of mixtures with a polyethylene fraction of 20% or less proceeds without the formation of a significant amount of products of incomplete decomposition of hydrocarbon chains. Thermogravimetric and calorimetric data are compared with data from mass spectrometric analysis of decomposition products. These data indicate competition between the oxidation and thermal cracking of polyethylene. The presence of biomass due to its high reactivity contributes to an increase in the proportion of oxidation in the total decomposition of polyethylene.

Oxidative cracking of three to five-member ring polycyclic aromatic hydrocarbons in subcritical and supercritical water

Polycyclic aromatic hydrocarbons (PAH) are refractory structures common in heavy hydrocarbons. Thermal cracking in supercritical water (SCW) is limited but PAH can be completely oxidised if an oxidant is added. By restricting oxidant supply to substoichiometric amounts, this study aims to achieve partial oxidation as a route to useful chemicals, such as mono- and bi-aromatics. Oxidative cracking reactions of anthracene, pyrene and benzo[a]pyrene in subcritical and SCW were studied. PAH conversions well above 90 % were achieved along a fast heating ramp in a batch reactor. This quick initial oxidation took place predominantly in inner rings, weakening the aromatic structure and increasing cracking reactivity. This oxidation-cracking pathway became dominant in the SCW region, producing mostly oxygenated compounds with fewer aromatic rings. On the other hand, competing reactions leading to polymerization were favoured in the subcritical water region. PAH reactivity was found to follow the order anthracene > benzo[a]pyrene > pyrene.

Effect of Heat Treatment on Isothermal Oxidation of Fe-33Ni-18Cr Alloy at 1000°C

This research study was focused on the effect of heat treatment on the isothermal oxidation of Fe-33Ni-18Cr alloy at 1000 °C. The Fe-33Ni-18Cr alloy was undergone heat treatment at three different temperatures, namely 1000 °C, 1100 °C and 1200 °C for 3 hours soaking time followed by water quench to vary the grain size of the alloy. The heat-treated alloys was prepared for further isothermal oxidation test. The heat-treated alloys was ground by using several grit of silicon carbide papers as well as weighed by using analytical balance and measured by using Vernier caliper before the oxidation test. The heat-treated Fe-33Ni-18Cr alloys was isothermally oxidized at 1000 °C for 150 hours exposure time. The characterization of the oxidized samples was carried out using optical microscope and scanning electron microscope (SEM). The heat treatment result shows that, increasing the heat treatment temperature was increased the average grain size of the alloy. The kinetics of oxidation was followed the parabolic rate law which represent the diffusion-controlled oxide growth rate. Fine grain structure of 1000i-1000 sample shows minimum weight gain and lower oxidation rate compared to samples of 1000i-1100 and 1000i-1200. On the other hand, 1000i-1100 and 1000i-1200 samples indicate the formation of oxide spallation and crack propagation on the oxidized surface, respectively.

Characterisation of deuterium distributions in corroded zirconium alloys using high-resolution SIMS imaging

Hydrogen diffusion through the oxide grown on Zr alloys by aqueous corrosion processes plays a critical role in determining the rate of hydrogen pickup (HPU) which can result in embrittlement of fuel cladding and limit the burnup of the nuclear fuel it encapsulates. Mapping the hydrogen/deuterium distributions in these oxide layers, especially in the barrier layer close to the metal/oxide interface, is a powerful way to understand the mechanism of both oxidation and hydrogen pickup. Here we have characterised by high-resolution SIMS analysis the deuterium distribution in oxide layers on a series of Zr alloys, including autoclave-oxidised Zircaloy-4, Zr-1Nb and Zr-2.5Nb alloys, and in-flux and out-of-flux corroded Zr-2.5Nb samples. Pre-transition Zircaloy-4 samples show a high deuterium trapping ratio in the oxide and a higher diffusion coefficient than in oxides on the Nb-containing samples. Neutron irradiation increases the deuterium diffusion coefficient, the deuterium concentration in the oxide and the pickup fraction in Zr-2.5 Nb samples. Comparative NanoSIMS and EDX/SEM analysis demonstrates that the deuterium is not preferentially trapped at second phase particles in the oxides on any of the alloys studied, but there is direct evidence for trapping at the surfaces of small oxide cracks especially in Zircaloy-4 samples. The high resolution mapping of these hot-spots in 3D can provide unique information on the mechanisms of hydrogen uptake, and suggests that the development of interconnected porosity in the oxide may be the critical rate-determining mechanism that controls HPU in the aqueous corrosion of zirconium alloys in water-cooled reactors.

Zeolite–Perovskite Composites as Effective Redox Catalysts for Autothermal Cracking of n-Hexane

This study reports highly effective, multifunctional ZSM5/CaMnO3@Na2WO4 composite redox catalysts for redox oxidative cracking (ROC) of n-hexane. Compared to the previously reported redox catalysts...

Erosion studies of Plasma-Sprayed NiCrBSi, Mo and Flyash Cenosphere coating

The erosion studies of plasma sprayed NiCrBSi / Mo / Flyash Cenosphere and NiCrBSi / Flyash Cenosphere on Superni 76 at room temperature for 30° and 90° impact angle were studied. The microstructure, adhesion properties, microhardness and porosity were investigated. Using SEM, EDS and EDAX techniques, the effect of phase change in the coating during the erosion was analyzed. The NiCrBSi/Mo/Cenosphere coating exhibits greater erosion resistance, and its loss of volume accounting nearly to 50% of the NiCrBSi / Cenosphere coating. Compared to a 90° impact angle, the smallest erosion loss was observed at 30°. The erosion process assessed using SEM micrographs showed that the coating suffered ductile fracture, exhibited acute deformation and had abnormal oxide cracks. The enhanced metal oxide has a shielding effect, can resist erosion, and thus has better erosion resistance.

Acceleration of Environmentally Assisted Cracking Initiation of the Type 316L Steel in High-Temperature Water and Hydrogenated-Steam Vapor Environments

Environmentally assisted cracking of solution-annealed Type 316L austenitic stainless steel with two different surface treatments (polished versus ground) was investigated using the constant extension rate tensile test methodology in high-pressure water at 350°C and low-pressure H2-steam vapor at 350°C, 400°C, 440°C, and 480°C, while maintaining electrochemical corrosion potentials in the NiO stability regime. Flat tapered specimens were used to indentify the threshold stress for cracking (∼400 MPa) under these environmental conditions. Intensive oxidation and typical intergranular cracks were observed to initiate from the polished surface at 400°C and 440°C, whereas wavy cracks initiated on the ground surface. The results indicate that the ultrafine-grained layer formed adjacent to the ground surface effectively suppressed intergranular crack initiation under these test conditions. The slow loading under H2-steam vapor at 400°C under the oxidizing condition (NiO) was found to be a suitable high-accelerated test to study early stages of the cracking.

Oxidative Dehydrogenation of Propane over Ni–Al Mixed Oxides: Effect of the Preparation Methods on the Activity of Surface Ni(II) Species

4Ni–Al layered double hydroxide (LDH) precursors were prepared by the following three methods: constant pH coprecipitation, variable pH coprecipitation and urea hydrolysis. The 4Ni–Al mixed metal oxide (MMO) catalysts were obtained by the calcination of LDH precursors at 600 °C, and their catalytic performances in ODHP from 350 to 550 °C were tested. The 4Ni–Al MMO from the urea hydrolysis method showed a higher and more stable propylene selectivity of ca. 40% with propylene yield of ca.11% at 500 °C, and that from the constant pH coprecipitation method was followed, while oxidative cracking of propane occurred on the 4Ni–Al MMO from the variable pH coprecipitation method. It is considered to be closely related to the dispersion and stability of the surface Ni(II) species through comprehensive analysis of XRD, N2-adsorption-desorption, TEM, XPS, H2-TPR and In-situ electrical conductivity. The urea hydrolysis method with a low salt concentration, leading to an excellent stability of the surface Ni(II) species at high reaction temperature, should be selected to prepare Ni–Al MMO catalysts for ODHP instead of the traditional variable pH coprecipitation method with a high salt concentration.

Y2O3 modified Au-La2O3 nanorod catalysts for oxidative cracking of n-propane

La2O3 and 0.2Au-La2O3 nanorod samples were synthesized by hydrothermal and chemical reduction routes respectively. The synthesized 0.2Au-La2O3 nanomaterial was modified with 1, 3, 5 and 7 wt% of Y2O3 by impregnation method. Powder XRD, FT-IR spectroscopy, FE-SEM, N2-physisorption, XPS, H2-TPR and O2-TPD techniques were utilized to evaluate the physico-chemical characteristics of the synthesized materials The XRD, SEM analyses revealed that the synthesized samples possessed small crystallite sizes with rod and spherical type morphologies. The XPS analysis indicating that the gold metal particles are well dispersed on the surface of the La2O3 nanorods. The efficacy of Y2O3 supported 0.2Au-La2O3 samples for catalytic oxidative cracking of n-propane was also studied. It was observed that Y2O3 loading had an impact on the n-propane conversion and olefins selectivity. Highest activity (78% n-propane conversion, 72% olefins selectivity) was observed in case of 5Y-0.2Au-La2O3 sample at 600 °C. The H2-TPR, O2-TPD and acidity analyses results revealed that 5Y-0.2Au-La2O3 sample is easily reducible, possessed more number of Lewis acid sites and mobile oxygen species. Therefore, the combination of these characteristics are responsible for the superior activity of 5Y-0.2Au-La2O3 catalyst. In addition, the synthesized catalysts showed stable catalytic n-propane oxidative cracking activity for 24 h without considerable deactivation.

Amphiphilic Carbon Quantum Dots as a Bridge to a Pseudohomogeneous Catalyst for Selective Oxidative Cracking of Alkenes to Aldehydes: A Nonmetallic Oxidation System.

The oxidative cleavage of alkenes to the corresponding aldehydes using new amphiphilic carbon quantum dots (A-CQDs) as a pseudohomogeneous carbocatalyst is achieved for the first time through green and sustainable chemical processes. In this work, we successfully design a recyclable pseudohomogeneous catalyst based on A-CQDs, which is decorated with 1-aminopropyl-3-methyl-imidazolium chloride and stearic acid. The functionalization is conducted to introduce a hydrophilic/hydrophobic functionality on the surface of the catalyst to achieve high catalyst availability in polar and nonpolar media with the green goal of eliminating organic (co)solvents and additives. This amphiphilic carbocatalyst provides high mass transferability to the biphasic system, which is beneficial to promoting the oxidative cracking of a variety of olefins into corresponding aldehydes with a substrate/A-CQD ratio of 150. Around 87% of the substrates are converted to the related aldehydes using the carbocatalyst in the presence of H2O2, in pure water, without using a phase-transfer catalyst or any additives and organic solvents, which is comparable with the current metal-based cleavage systems. Surprisingly, A-CQDs exhibit high catalytic activity for the scission of electron-deficient C═C bond of coumarin derivatives, accompanied by the cleavage of C-O bonds to produce the corresponding salicylaldehyde derivatives without overoxidation to acid. As a brief conclusion, A-CQDs exhibit high conversion efficiency without significant loss of activity even after six catalytic cycles. The conversion of alkenes into aldehydes is fast and high-throughput without overoxidation to acids and is accompanied by excellent solubility and stability in various solvents. Moreover, the product and the catalyst are recoverable from the reaction medium by simple extraction. So, this pseudohomogeneous carbocatalyst promises new horizons in imminent "catalytic age". All in all, this paper provides a significant and novel advancement in carbocatalyst chemistry.

The obvious advantage of amino-functionalized metal-organic frameworks: As a persulfate activator for bisphenol F degradation

In this study, two iron-based metal-organic framework compounds (MOFs), were used and compared as catalysts for persulfate (PS) activation to degrade bisphenol F (BPF). The outstanding advantage of using amino-functionalized MOFs in the catalytic system was verified under different reaction conditions, and the mechanism was explored. The results indicated that NH2-MIL-101(Fe)/PS system not only had a wide pH application range, but also possessed an excellent catalytic performance towards interference from the coexisting anions and humic acid. Density functional theory (DFT) calculations showed that, compared with MIL-101(Fe), the –NH2 modification could significantly improve the electronic conductivity of NH2-MIL-101(Fe) by enhancing its Fermi level (−4.28 eV) and binding energy to PS (−1.19 eV). The free radical quenching experiments were combined with electron paramagnetic resonance (EPR) confirmed that free radicals (SO4−, OH, O2−) worked together with the non-radical (1O2) reaction to remove 91% BPF within 40 min in the NH2-MIL-101(Fe)/PS system. The two proposed BPF degradation pathway were related to hydroxylation, oxidation and ring cracking. The toxicity of the BPF degradation intermediates as well as its final products were also evaluated.

Gold supported yttrium oxide nanorods for catalytic oxidative cracking of n-propane to light olefins

An alkali assisted hydrothermal method was utilized to synthesize Y2O3 nanorods. Gold (0.5, 1.0, 1.5 and 2.0 wt%) supported Y2O3 nanorods samples were prepared by chemical reduction method and the synthesized Au-Y2O3 nanomaterials were utilized as catalysts for oxidative cracking of n-propane. The bulk Y2O3 nanorods showed n-propane conversion of 20% with 25% light olefins (ethylene and propylene) selectivity at 600 °C. Significant enhancement in both n-propane conversion and olefins selectivity were observed after gold deposition. Gold (1.5 wt%) supported Y2O3 nanorods (1.5Au-Y2O3- NR) sample offered highest activity (75.5% conversion of n-propane and 90.3% olefins selectivity) at 600 °C. The different techniques such as elemental analysis, powder X-ray diffraction, FT-IR, FE-SEM, DR UV–vis, N2-physisorption, XPS and H2-TPR measurements were used to determine physico-chemical properties of the synthesized catalysts. The characterization results revealed an existence of synergetic effect between the gold and Y2O3-NR support due to strong metal-support interaction. The superior catalytic activity of 1.5Au-Y2O3-NR sample is due to the fact that this catalyst possessed more number of mobile oxygen species, large number of Lewis acidic sites and also Auδ+-O-Y species. Time on stream analysis indicated that gold supported Y2O3 nanorod catalysts exhibited considerable stable activity for 24 h with slight loss of performance due to agglomeration of gold particles.

High-performance VOx on SrO-γAl2O3 catalyst for oxidative cracking of n-hexane to light olefins under anaerobic environment

Novel VOx/SrO-γAl2O3 catalysts have been investigated in oxidative cracking of n-hexane to light olefins. The supports, with different SrO/γAl2O3 ratios, were synthesized by a surfactant-free method, while VOx was incorporated on SrO-γAl2O3 by impregnation. NH3-TPD showed that the acidity of the catalysts decreased with the increase of SrO. The incorporation of SrO also modified the reducibility (H2-TPR) of the catalysts. VOx appeared as amorphous polymeric species on the support, confirmed by XRD, Raman and FTIR analyses. The oxidative cracking of n-hexane was conducted by using a fluidized CREC Riser Simulator in absence of gas phase oxygen. Under the studied reaction conditions (525−600°C; 10−25s), the products contained mainly light olefins (ethylene, propylene and butenes), paraffins, and carbon oxides. Among the synthesized catalysts, VOx/SrO-γAl2O3 1:1 showed highest olefins selectivity (88%) at high n-hexane conversion (84%) because of its balanced acidity and moderate VOx-support interactions.

Characterisation of Deuterium Distributions in Corroded Zirconium Alloys Using High-Resolution SIMS

Hydrogen diffusion through the oxide grown on Zr alloys by aqueous corrosion processes plays a critical role in determining the rate of hydrogen pickup which can result in embrittlement of fuel cladding and limit the burnup of the nuclear fuel it encapsulates. Mapping the hydrogen/deuterium distributions in these oxide layers, especially in the barrier layer close to the metal/oxide interface, is a powerful way to understand the mechanism of both oxidation and hydrogen pickup. Here we have characterised by high-resolution SIMS analysis the deuterium distribution in oxide layers on a series of Zr alloys, including autoclave-oxidised Zircaloy-4, Zr-1Nb and Zr-2.5Nb alloys, and in-flux and out-of-flux corroded Zr-2.5Nb samples. Pre-transition Zircaloy-4 samples show a high deuterium trapping ratio in the oxide and a higher diffusion coefficient than in oxides on the Nb-containing samples. Neutron irradiation increases the deuterium diffusion coefficient, the deuterium concentration in the oxide and the pickup fraction in Zr-2.5 Nb samples. Comparative NanoSIMS and EDX/SEM analysis demonstrates that the deuterium is not preferentially trapped at SPPs in the oxides on any of the alloys studied, but there is direct evidence for trapping at the surfaces of small oxide cracks especially in Zircaloy-4 samples. The high resolution mapping of these hot-spots in 3D can provide unique information on the mechanisms of hydrogen uptake, and suggests that the development of interconnected porosity in the oxide may be the critical rate-determining mechanism that controls HPU in the aqueous corrosion of zirconium alloys in water-cooled reactors.