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Lower olefins are hydrocarbons that are widely used in the chemical industry, and can be generated from syngas by the ‘Fischer–Tropsch to olefins’ process; here, a new catalyst is described that can generate lower olefins from syngas with high selectivity, with little formation of undesirable methane. Lower olefines—and not much methane—from biomass The lower olefins—chiefly ethylene, propylene and butylene—are starting materials for many plastics and other industrial products. They are usually obtained by cracking hydrocarbon feedstocks, so as petroleum reserves become depleted the urgency to switch to alternative feedstocks such as biomass increases. The 'Fischer–Tropsch to olefins' (FTO) process produces lower olefines from syngas—a mixture of hydrogen and carbon monoxide derived from biomass, coal and natural gas—but at the same time produces large amounts of unwanted methane. Here Liangshu Zhong and colleagues describe a new catalyst for the FTO conversion. Formed from cobalt carbide nanoprisms, the catalyst is active in mild reaction conditions, is highly selective for lower olefins and, critically, produces very little methane. Lower olefins—generally referring to ethylene, propylene and butylene—are basic carbon-based building blocks that are widely used in the chemical industry, and are traditionally produced through thermal or catalytic cracking of a range of hydrocarbon feedstocks, such as naphtha, gas oil, condensates and light alkanes 1 , 2 . With the rapid depletion of the limited petroleum reserves that serve as the source of these hydrocarbons, there is an urgent need for processes that can produce lower olefins from alternative feedstocks 3 , 4 , 5 , 6 , 7 , 8 , 9 . The ‘Fischer–Tropsch to olefins’ (FTO) process has long offered a way of producing lower olefins directly from syngas—a mixture of hydrogen and carbon monoxide that is readily derived from coal, biomass and natural gas 3 , 4 , 5 , 6 , 7 . But the hydrocarbons obtained with the FTO process typically follow the so-called Anderson–Schulz–Flory distribution, which is characterized by a maximum C 2 –C 4 hydrocarbon fraction of about 56.7 per cent and an undesired methane fraction of about 29.2 per cent (refs 1 , 10 , 11 , 12 ). Here we show that, under mild reaction conditions, cobalt carbide quadrangular nanoprisms catalyse the FTO conversion of syngas with high selectivity for the production of lower olefins (constituting around 60.8 per cent of the carbon products), while generating little methane (about 5.0 per cent), with the ratio of desired unsaturated hydrocarbons to less valuable saturated hydrocarbons amongst the C 2 –C 4 products being as high as 30. Detailed catalyst characterization during the initial reaction stage and theoretical calculations indicate that preferentially exposed {101} and {020} facets play a pivotal role during syngas conversion, in that they favour olefin production and inhibit methane formation, and thereby render cobalt carbide nanoprisms a promising new catalyst system for directly converting syngas into lower olefins.

Understanding the structures and reaction mechanisms of interfacial active sites in the Fisher-Tropsch synthesis reaction is highly desirable but challenging. Herein, we show that the ZrO 2 -Ru interface could be engineered by loading the ZrO 2 promoter onto silica-supported Ru nanoparticles (ZrRu/SiO 2 ), achieving 7.6 times higher intrinsic activity and ~45% reduction in the apparent activation energy compared with the unpromoted Ru/SiO 2 catalyst. Various characterizations and theoretical calculations reveal that the highly dispersed ZrO 2 promoter strongly binds the Ru nanoparticles to form the Zr-O-Ru interfacial structure, which strengthens the hydrogen spillover effect and serves as a reservoir for active H species by forming Zr-OH* species. In particular, the formation of the Zr-O-Ru interface and presence of the hydroxyl species alter the H-assisted CO dissociation route from the formyl (HCO*) pathway to the hydroxy-methylidyne (COH*) pathway, significantly lowering the energy barrier of rate-limiting CO dissociation step and greatly increasing the reactivity. This investigation deepens our understanding of the metal-promoter interaction, and provides an effective strategy to design efficient industrial Fisher-Tropsch synthesis catalysts. Understanding the structures of interfacial active sites is crucial in heterogeneous catalysis. Here the authors demonstrate that a ZrO 2 -Ru interface site significantly enhances reactivity in the Fischer-Tropsch to olefins process by altering the H-assisted CO dissociation route due to the presence of hydroxy species associated with Zr-OH*.

Syngas conversion serves as a competitive strategy to produce olefins chemicals from nonpetroleum resources. However, the goal to achieve desirable olefins selectivity with limited undesired C1 by-products remains a grand challenge. Herein, we present a non-classical Fischer-Tropsch to olefins process featuring high carbon efficiency that realizes 80.1% olefins selectivity with ultralow total selectivity of CH 4 and CO 2 (<5%) at CO conversion of 45.8%. This is enabled by sodium-promoted metallic ruthenium (Ru) nanoparticles with negligible water-gas-shift reactivity. Change in the local electronic structure and the decreased reactivity of chemisorbed H species on Ru surfaces tailor the reaction pathway to favor olefins production. No obvious deactivation is observed within 550 hours and the pellet catalyst also exhibits excellent catalytic performance in a pilot-scale reactor, suggesting promising practical applications. Zhong et al report sodium-promoted metallic Ru nanoparticles for the direct production of olefins from syngas with ultrahigh carbon efficiency where the total selectivity of undesired CH 4 and CO 2 is suppressed to only 5% for over 500 hours on stream.

The limited surface coverage and activity of active hydrides on oxide surfaces pose challenges for efficient hydrogenation reactions. Herein, we quantitatively distinguish the long-puzzling homolytic dissociation of hydrogen from the heterolytic pathway on Ga 2 O 3 , that is useful for enhancing hydrogenation ability of oxides. By combining transient kinetic analysis with infrared and mass spectroscopies, we identify the catalytic role of coordinatively unsaturated Ga 3+ in homolytic H 2 dissociation, which is formed in-situ during the initial heterolytic dissociation. This site facilitates easy hydrogen dissociation at low temperatures, resulting in a high hydride coverage on Ga 2 O 3 (H/surface Ga 3+ ratio of 1.6 and H/OH ratio of 5.6). The effectiveness of homolytic dissociation is governed by the Ga-Ga distance, which is strongly influenced by the initial coordination of Ga 3+ . Consequently, by tuning the coordination of active Ga 3+ species as well as the coverage and activity of hydrides, we achieve enhanced hydrogenation of CO 2 to CO, methanol or light olefins by 4-6 times. Zhu et al. report a quantitative and time-resolved analysis of hydrogen activation on Ga 2 O 3 , specifically shedding light on the long-standing puzzle of homolytic dissociation as opposed to the heterolytic pathway on oxides.

Syngas conversion to fuels and chemicals is one of the most challenging subjects in the field of C1 chemistry. It is considered as an attractive alternative non-petroleum-based production route. The direct synthesis of olefins and alcohols as high value-added chemicals from syngas has drawn particular attention due to its process simplicity, low energy consumption and clean utilization of carbon resource, which conforms to the principles of green carbon science. This review describes the recent advances for the direct production of lower olefins and higher alcohols via syngas conversion. Recent progress in the development of new catalyst systems for enhanced catalytic performance is highlighted. We also give recommendations regarding major challenges for further research in syngas conversion to various chemicals.

Microseismic data and production logs in our study area have confirmed asymmetric developments of the stimulation rock volume in shales with respect to the wellbore, while severe casing deformation problems have been reported frequently in this area. Here, we propose a systematic methodology to investigate the possibility of casing failure due to strong shear stresses induced by asymmetric stimulated zones. A mechanical earth modeling (MEM) is initially performed to determine the in situ stress field in the target layer before fracturing by incorporating the existing geological features, logging data, and rock anisotropy. Then, we provide a computationally cheap and efficient estimation for stimulated rock volume of each stage by considering the possible overlaps in adjacent stages based on the clustered microseismic clouds. Using this approach, a reservoir‐scale 3D coupled model tied to a more detailed near‐wellbore part incorporating the casing string and the cement sheath is established to simulate the development of stimulation zones, stress redistribution, and their impacts on casing deformation as each stage fracturing treatment chronologically goes on. Our numerical results indicate that continuous redistribution and re‐orientation of stress field near the borehole are tracked during pumping the treatment which reveals formation of some pockets of tensile stresses along and around the wellbore. Asymmetric stimulations are observed to generate strong shear stress on the suspended casing. These shear forces result in deflection and S‐shape deformations accompanied with cross‐sectional ovality. Some regions receive repeating treatments, which results in intensifying formation stress heterogeneity and worsen casing deformation severity. The calculation results are compared with measurement of multi‐finger imaging tool (MIT) to validate the accuracy. Our analysis has indicated that simply increasing the flexural strength by increasing thickness of casing cannot radically mitigate casing deformation problems. This paper presents a novel workflow for a coupled modeling of casing deformation during hydraulic fracturing operations, while current modeling efforts assume symmetric bi‐wing fracture geometries. Asymmetric stimulation treatments may induce significant shear forces on the wellbore casing and compromise its integrity. In this paper, we discuss the mechanism behind this problem and how to avoid this problem by changing perforation spacing.

A large number of casing failures occur during the volume fracturing operation of shale gas, making normal completion stimulations impossible. To solve this problem, rock mechanical experiments and numerical simulation experiments are carried out in this article. It is found that the macroscopic rock mechanical strength reduces most when the crack angle of fissured rock in Longmaxi Formation is 45°, and it reduces stably when the number of cracks increases to 8. The elasticity modulus ratio, yield strength ratio, and compressive strength ratio are 0.70, 0.71, and 0.68, respectively, based on which this article establishes the finite element model for shale gas well X201. Then, the secondary development realizes the dynamic adjustment of the rock mechanical properties during the fracturing. The correctness of method and model in the article is verified through comparing the simulated calculation of casing deformation and the field multi-arm caliper logging data. The casing failure mechanism is revealed, providing a theoretical basis for the prevention of casing failure caused by shale gas fracturing.

At the high or extra-high temperatures in a natural gas oilfield, where the premium connection is employed by casing, gas leakage in the wellbore is always detected after several years of gas production. As the viscoelastic material’s mechanical properties change with time and temperature, the relaxation of the contact pressure on the connection sealing surface is the main reason for the gas leakage in the high-temperature gas well. In this article, tension-creep experiments were conducted. Furthermore, a constitutive model of the casing material was established by the Prony series method. Moreover, the Prony series’ shift factor was calculated to study the thermo-rheological behavior of the casing material ranging from 120°C to 300°C. A linear viscoelastic model was implemented in ABAQUS, and the simulation results are compared to our experimental data to validate the methodology. Finally, the viscoelastic finite element model is applied to predict the relaxation of contact pressure on the premium connections’ sealing surface versus time under different temperatures. And, the ratio of the design contact pressure and the intending gas sealing pressure is recommended for avoiding the premium connections failure in the high-temperature gas well.

Because marine riser is under complex ocean current environment, fatigue damage tends to happen due to vortex-induced vibration, which has a strong impact on the safety issue of deepwater drilling and completion. Vortex-induced vibration (VLV) induced by non-uniform flow loads on deep water riser coupling in complex Marine environments has been studied relatively infrequently at home and abroad. Therefore, CFD-FEM bidirectional fluid-solid coupling method was used to establish a vortex-induced vibration model of 1500m deep water riser and non-uniform flow in waves and currents. Vortex-induced vibration and mechanical behavior of riser in transverse and flow direction were studied from riser motion characteristics, tension factors and other aspects. The results show that the danger zone of vortex-induced vibration of riser under the action of non-uniform flow occurs in one third of the upper end. Increasing the tension can increase the riser's natural frequency and reduce the amplitude of vortex-induced vibration, but may aggravate the riser's high stress and low cycle fatigue damage.

The casing is subjected to complicated forces underground, and the threaded joint of the casing is the weak link of the casing. becoming more and more severe, various kinds of failure accidents often occur in practical use. Therefore, in view of the casing thread fracture failure during the process of volumetric fracturing in well W of an oil field. The finite element model of 5-1/2\"API casing long round threaded joint was established in this paper, ABAQUS software was used to simulate and analyze the stress and deformation of casing thread under the loading state of overlock, axial tension and pressure, and fracturing internal pressure. The results show that the stress distribution of teeth is reasonable. Under the condition of axial tension and compression, the maximum stress of casing thread exceeds the yield strength into plasticity and causes damage. However, when fracturing and stimulation technology is implemented, the stress of the collar and casing body increases significantly, and the fracture is caused by fatigue and extended fracture under the alternating fracturing load. The finite element analysis results are consistent with the field failure results. Study the influence of downhole complex working condition on casing thread by simulation, which is of great significance to the protective casing.