Undesired Deposition Research Articles

The robust catalysts (Ni1−x–Mox/doped ceria and Zn1−x–Mox/doped ceria, x = 0.1 and 0.3) for efficient natural gas reforming in solid oxide fuel cells

Nickel is a promising catalyst in Solid Oxide fuel cell (SOFC) due to its electrocatalytic performance, however, the practical utilization of Ni-based materials is hindered by the undesirable carbon deposition during methane decomposition. Herein, molybdenum is incorporated into the Ni- and Zn-based cermets (Ni1−x–Mox/GDC and Zn1−x–Mox/GDC, x = 0.1 and 0.3) to enhance electrocatalytic properties and avoid the carbon deposition during cell operation. The desired composites are synthesized by the impregnation method and adopted as anode in SOFCs. The catalytic activity for methane oxidation has been significantly improved due to the introduction on Mo, which hindered the carbon deposition due to higher graphitization and abundant active sites accessible to fuel. The detailed Raman spectroscopy and conductivity analysis revealed that addition of Mo reduced the amount of deposited carbon and enhanced the electrical conductivity. By using natural gas, as a fuel, the as-prepared Mo-doped Ni–GDC rendered a maximum power density of 690 mW cm−2 at 600 °C. It is worth mentioning that the achieved stable power density is one of the best in existing literature. The current study presents a novel strategy to improve the catalytic behavior of electrode materials and demonstrate the optimal performance at low operating temperature.

On the varieties of build features during multi-layer laser directed energy deposition

Laser directed energy deposition (DED) is an additive manufacturing (AM) process involving progressive deposition of individual layers to form a multi-layer build. A deep understanding of the spatiotemporal variations of the entire build, individual tracks and layers, and the molten pool is critical to the control of undesired deposition profiles and the production of targeted laser DED components. In this work, diverse build features during multi-layer laser DED of Ti-6Al-4 V are systematically explored on multiple scales via advanced 3D numerical modeling and corresponding experiments for various process conditions. The layer wise increments on the build top are demonstrated with distinct additive features of individual layers in transverse and longitudinal sections. The results show that the layer bottom boundaries vary from concave to flat and further convex at higher layers. Moreover, the influences of scanning strategies on the deviations of build profiles are investigated considering the reinforcement or the compensation of the uneven layer geometries along the scanning direction. The underlying mechanisms are revealed through dimensionless numbers and the transport phenomena of energy, mass, and momentum in the freeform molten pool during the multi-layer deposition process. The scientific findings provide useful insight for the deep understanding of the physical processes, and support further researches on microstructure evolution and resultant mechanical properties of the DED components.

Scalable synthesis of zeolite-templated ordered microporous carbons without external carbon deposition for capacitive energy storage

Abstract Zeolite-templated carbons (ZTCs) have unique ordered microporous structures composed of 3-dimensionally connected graphene nanoribbons and buckybowl-like frameworks. ZTCs can exhibit extra-large surface areas, narrow micropore size distributions, and electrical conductivity, which make them promising for adsorption, catalysis, and energy storage. However, the synthesis of ZTCs still remains a great challenge when the synthesis scale is larger than just a few grams. Carbon deposition within narrow zeolite micropores is diffusion-limited, and unwanted dense carbon layers are often deposited at the external surface of zeolite, substantially diminishing ZTCs' structural properties and performances in various applications. In this study, we conducted the large-scale synthesis of ZTCs (>80 g) in a bubbling fluidized bed, which enables efficient mass/heat transfer. Compared to conventional synthesis in a fixed bed, ZTCs with superior structural properties could be synthesized in much shorter time. The resultant ZTCs showed ordered microporous structures with large surface areas (~3000 m2 g−1) and microporosity (~1.1 cm3 g−1). Most importantly, these ZTCs were free of undesirable external carbon deposition, which greatly diminishes the mass transfer of guest molecules (e.g., electrolytes) into the micropores. As a result, the ZTCs showed superior electrical double-layer capacitance compared to those synthesized in a typical fixed bed.

Heat transfer and fouling deposition investigation on the titanium coated heat exchanger surface

Fouling is the undesired deposition on heat exchanger surfaces which enhance heat transfer resistances and retard heat exchanger performance. This paper investigates fouling mitigation of calcium carbonate by the application of coatings on SS316L heat exchanger. Titanium (Ti) was selected as coating material due to its high resistance to corrosion and good surface adhesion. Physical vapor deposition method was adopted to coat Ti on the SS316L surface. Heat transfer investigation at different flow rates were conducted to observe the effect of coating and then fouling experiments were carried out to investigate the deposition of Calcium Carbonate to the coated and uncoated surfaces. The test section was taken under microscopic investigation to study the surface texture before and after the fouling effect. It was observed that the Ti coated SS316L surface of heat exchanger surface experienced less corrosion, enhanced heat transfer and reduced fouling deposition.

In situ constructing lithiophilic NiFx nanosheets on Ni foam current collector for stable lithium metal anode via a succinct fluorination strategy

Metallic lithium is considered as the optimal anode material for the high-energy–density rechargeable lithium-based battery. However, the commercial application of Li metal anode is plagued by uncontrollable dendrites growth and unstable SEI layer derived from the nonuniform nucleation and undesired deposition process. Herein, a hybrid 3D porous Ni foam (NF) current collector decorated by nanostructured lithiophilic layer of interconnected NiFx nanosheets is firstly synthesized by a convenient one-step fluorination strategy. Benefiting from superior lithiophilicity, the NiFx nanosheets can successfully decrease the Li nucleation barrier and act as uniformly distributed nucleation sites for inducing the homogeneous Li deposition. In addition, the interconnected morphology of the NiFx nanosheets and the 3D porous structure of the NF effectively reduce the local current density of the electrode and thus alleviate the dendrites formation. Moreover, a LiF-enriched SEI layer in situ generated from the electrochemical reaction also facilitates the smooth Li plating. As a result, this 3D hybrid NiFx@NF current collector demonstrates dendrite-suppressed Li deposition morphology and excellent stripping/plating reversibility, presenting significantly enhanced Coulombic efficiency of ~ 98% over 450 cycles at 1 mA cm−2. Remarkably, symmetric cell with Li@NiFx@NF anode achieves a prolonged cycling lifespan over 1300 h together with a low overpotential of ~ 20 mV at 1 mA cm−2 under the cycling capacity of 1 mAh cm−2. Furthermore, excellent cycling performance and rate capability of the Li@NiFx@NF anode are also realized in full cells when coupled with LiFePO4 and Li4Ti5O12 cathodes. Our work not only provides an expeditious fluorination strategy to construct 3D fluorinated compound but also illustrates the superiority of synergetic design of lithiophilic sites plus LiF-enriched SEI layer for the current collector of Li metal anode.

Remnant Coal Detection System

This paper describes the development and successful implementation of a system designed to detect coal deposits remaining in coal train wagons after unloading (dumping). These undesirable coal deposits constitute both small residual amounts of “carryback”, but also larger “hang-ups” of significant volume that have failed to discharge. The system was originally developed simply to detect and record volumes of carryback, as part of an effort to characterise the extent of the problem for the coal transport industry, but was then enhanced to provide real-time feedback of large hang-ups so that they could be discharged prior to the wagons exiting the dump station. The paper describes the hardware and processing systems used in the system, including the different strategies employed to ensure a reliable detection system. The system has now been installed and operated in a production environment at three dump stations across two different coal terminals, and a case study of the results from one of these dump stations is presented. Automating remnant coal detection at dump stations provides short interval control to minimise potential hazards and downtime, and historical data that may be integrated into existing data platforms and analysed for productivity, environmental, and safety planning insights.

Catalyst-assisted DBD plasma for coupling of methane: Minimizing carbon-deposits by structured reactors

Non-oxidative coupling of methane has been performed in DBD plasma reactors with a catalytic layer with varying thickness loaded on the reactor wall. These structured reactors allow to study the effect of the thickness of the catalyst layer, including the blank plasma reactor, without significant modification of plasma properties, SEI and residence time. Moreover, it allows analysis of the catalytic effect of Pd/Al2O3. The catalyst layer decreases the methane conversion only mildly, which is attributed to hydrogenation of CHx radicals at the outer surface of the catalyst layer. This results in typically 34 % methane conversion at 2.8 W at room temperature with 6% CH4 in Ar, independently of the layer thickness. In contrast, the thickness of the catalyst layer strongly influences the product distribution, assigned to hydrogenation of acetylenes at external and internal surfaces in the catalyst layer. The formation of undesired deposits is suppressed by a factor of 2 with value-added hydrocarbons selectivity of 70 % and a carbon balance of 93 %. In addition, catalytic-wall reactors was compared with packed bed reactors. The synergistic effect is much more evident in the structured reactor than in the packed bed reactor, independently of the position of the catalytic bed.

Single-atom scale metal vacancy engineering in heteroatom-doped carbon for rechargeable zinc-air battery with reduced overpotential

Metal-air batteries have drawn great attention in the past decade due to their high energy density and low cost. However, several challenges remain in the development of such promising devices, including slow kinetics of the cathodic reaction and undesirable deposition of metal oxide on air cathode. Herein, as a proof of concept, we show single-atom scale metal vacancy engineering in heteroatom-doped carbon cathode to enable high-performance zinc-air battery with reduced overpotential. Density functional theory calculations indicate that metal vacancy-induced pyridinic-N can tailor the electronic structure and thus facilitate the catalytic reaction. The single-atom dispersed Fe–N–C catalyst with optimized Fe vacancies shows improved reactivity and the facilitated chemisorption of oxygen intermediates in the actual battery operation is directly observed by in-situ X-ray diffraction characterization. Moreover, the in-situ observation also indicates the absence of zinc oxide, which can be ascribed to strong Lewis basicity created by pyridinic-N that effectively prevents the access of zincate ions with negative charge and thus enables non-deposition of zinc oxide. Applying this strategy, the rechargeable zinc-air battery shows high reversibility and stability over 1000 cycles with negligible voltage gap change of only 0.04 V. This work not only affords valuable insights but also opens up new perspectives to develop high-performance metal-air batteries.

COMBUSTION ANALYSIS OF D-LIMONENE AS AN ADDITIVE TO DIESEL-BIODIESEL BLENDS IN COMPRESSION IGNITION ENGINES

Vegetable oils, when subjected to transesterification process generate “vegetable oils esters”, with similar properties as density, cetane number, heating values, air-fuel ratio. However, problems resulting from the higher viscosity, leads to a worst spraying and combustion, formation of undesirable deposits on engine parts and contamination of the lubricant oil. Due to these problems, it is interesting to study an additive, also derived from biomass, to improve the characteristics of biodiesel for a suitable use in diesel engines. This paper proposes an additive (d-limonene obtained from orange peel) and preliminary results obtained from the tests in a stationary diesel engine fueled with mixtures of diesel/biodiesel/d-limonene, in different concentration to compare with a regular diesel-biodiesel blend and analyzes the influence of the additive on the combustion process. The diesel oil used was purchased from BR supply network (containing 7% biodiesel in its composition) and two blends with different concentrations of the additive (1% and 3% of d-limonene) were prepared and tested. Diesel without additive was also tested. The effects of the DS10 addititivation with d-limonene in the combustion process of a diesel engine have been analyzed, the results obtained were satisfactory showing the positive effects in the combustion process with the addition of d-limonene in diesel-biodiesel blends, decreasing the ignition delay around 2 degrees and showing an improvement in the cetane number of the fuel.

Joint SoC and SoH Estimation for Zinc–Nickel Single-Flow Batteries

The zinc–nickel single-flow battery is a new and special type of flow battery with a number of promising features, such as membrane free and high scalability, and thus has attracted substantial interests in recent years. However, the cyclability of alkaline zinc cells is rather poor, with sharpened capacity degradation resulted from undesirable zinc deposition formation. Yet, little has been done so far to investigate how to effectively and reliably manage this new type of battery. In this article, an open-circuit-voltage estimator based online joint estimation of both the state of charge (SoC) and the state of health (SoH) is proposed. A second-order equivalent circuit model is applied to improve the accuracy. Meanwhile, an extended Kalman filter with reduced state dimension is formulated to estimate the SoC assisted with the proposed estimator, which solves the increased complexity issue in a higher order model. An SoH indicator is then derived from capacity estimate and employed to determine the time for reconditioning maintenance, which is a key stage to update capacity and prolong service life. The method is finally applied to a bench-scale cell demonstrator, and the experimental results confirm the efficacy of the proposed method.

Overcoming Stability Problems in Microwave-Assisted Heterogeneous Catalytic Processes Affected by Catalyst Coking

Microwave-assisted heterogeneous catalysis (MHC) is gaining attention due to its exciting prospects related to selective catalyst heating, enhanced energy-efficiency, and partial inhibition of detrimental side gas-phase reactions. The induced temperature difference between the catalyst and the comparatively colder surrounding reactive atmosphere is pointed as the main factor of the process selectivity enhancement towards the products of interest in a number of hydrocarbon conversion processes. However, MHC is traditionally restricted to catalytic reactions in the absence of catalyst coking. As excellent MW-susceptors, carbon deposits represent an enormous drawback of the MHC technology, being main responsible of long-term process malfunctions. This work addresses the potentials and limitations of MHC for such processes affected by coking (MHCC). It also intends to evaluate the use of different catalyst and reactor configurations to overcome heating stability problems derived from the undesired coke deposits. The concept of long-term MHCC operation has been experimentally tested/applied to for the methane non-oxidative coupling reaction at 700 °C on Mo/ZSM-5@SiC structured catalysts. Preliminary process scalability tests suggest that a 6-fold power input increases the processing of methane flow by 150 times under the same controlled temperature and spatial velocity conditions. This finding paves the way for the implementation of high-capacity MHCC processes at up-scaled facilities.

High-Rate Cycling of Lithium-Metal Batteries Enabled by Dual-Salt Electrolyte-Assisted Micropatterned Interfaces.

We present a synergistic strategy to boost the cycling performance of Li-metal batteries. The strategy is based on the combined use of a micropattern (MP) on the surface of the Li-metal electrode and an advanced dual-salt electrolyte (DSE) system to more efficiently control undesired Li-metal deposition at higher current density (∼3 mA cm-2). The MP-Li electrode induces a spatially uniform current distribution to achieve dendrite-free Li-metal deposition beneath the surface layer formed by the DSE. The MP-Li/DSE combination exhibited excellent synergistic rate capability improvements that were neither observed with the MP-Li system nor for the bare Li/DSE system. The combination also resulted in the Li||LiMn2O4 battery attaining over 1 000 cycles, which is twice as long at the same capacity retention (80%) compared with the control cells (MP-Li without DSE). We further demonstrated extremely fast charging at a rate of 15 C (19.5 mA cm-2).

Polyvinyl Alcohol-Based Cryogels for the Oil Industry

The paper presents the results of studies of rheological properties of the initial viscous solutions of polyvinyl alcohol and ‘oil-in-water’ (O/W) emulsions. It is found that aqueous solutions of polymer and polymer-based colloidal systems have typical non-Newtonian properties. After the freeze-thaw cycle, the viscous liquid systems pass into a solid state of aggregation to form multicomponent cryogels with rubber-like structure. The elastic properties of two-component cryogels consisting of polyvinyl alcohol and water only, three-component compositions formed on the basis of an ‘aqueous PVA solution-mineral oil’ emulsion, and cryogels containing loose dispersed fillers are investigated. The physicochemical properties of the obtained elastic samples are studied. The prospects of application of cryogels for the oil producing well and road construction are outlined. A comparative analysis of physicomechanical properties of cryogels depending on the nature of the filler is carried out. In order to simulate the real conditions of oil field construction in the permafrost zone, samples of cryogels with solid dispersed fillers pre-wetted with oil are prepared and their mechanical and hydrophobic properties are investigated. Hydrophobic properties of cryogels make it possible to use them as waterproofing layer (membrane) in the construction of the asphalt pavement and insulation of the bottoms and walls of hydraulic structures. Cryogels can be recommended for use as polymer ‘pigs’ for removal of undesirable deposits in the pipeline during its cleaning or for pipeline pressure testing. In this case, ‘batching pigs’ are introduced to the boundary between hydrocarbon liquid and water.

Mechanical collapse as primary degradation mode in mandrel-free 18650 Li-ion cells operated at 0 °C

Low temperature charging of Li-ion batteries threatens undesired deposition of lithium dendrites which are often blamed for catastrophic, thermal runaway failures. This work identifies three distinct degradation modes experienced by 0 °C operated 18650 Li-ion batteries, revealing safety and performance risks beyond lithium plating. Two equivalently rated (2.6Ah) commercial cells from different vendors, one possessing a mandrel and one lacking, were cycled at 0 °C. Through a combination of techniques, it is identified that the first degradation mode is dominated by cell polarization at low temperature, causing lower coulombic efficiency and undesired side reactions. Next, mechanical deformation or jellyroll collapse occurs, followed by accelerated metal plating. However, in the mandrel-containing cell, physical constraint of the electrodes prevents both the deformation and metal plating modes. These degradation modes, difficult to isolate with electrochemistry alone, were diagnosed with non-destructive micro X-ray computed tomography and destructive physical analysis and confirmed with differential capacity assessment. The implication of the physical conditions induced by 0 °C operation on cell safety was assessed with accelerated rate calorimetry. Our observations emphasize the presence of thermo-mechano-electrochemical interplay in commercial cells operated in extreme conditions and assesses the safety implications of their coupling.

Effect of oscillating temperature and crystallization on graphene oxide composite pervaporation membrane for inland brine desalination

Membrane distillation (MD) for desalination experienced technical challenges when treating concentrated inland brine with high salinity under industrially-relevant oscillating temperature condition or solar desalination. In this study, we fabricated a composite membrane using graphene oxide (GO) and used it in a pervaporation (PV) process to tackle the issues encountered in the MD processes. The resultant GO composite membranes demonstrated fast water vapor transport through nano-channels between the GO interlayers. In addition, the smoother and negatively charged surface offered by the GO layer hindered the undesired crystal deposition on the membrane surface, and therefore giving a substantially improved performance than the MD process when operated under oscillating temperature. More importantly, the presence of divalent cations in inland brine led to a naturally-occurring crosslinking between the GO nanosheets that offered molecular sieving functionality to the GO layer, preventing the transport of salt ions, as well as GO swelling and therefore providing exceptional performance sustainability, especially under oscillating temperature condition. Interestingly, it was found that GO composite membrane in a PV process for desalination offered greater overall water productivity when operated under the oscillating temperature compared to the constant temperature. These GO composite membranes also demonstrated good performance stability after chemical cleaning and when exposed to minor contaminants found in inland brine such as humic acid.

Tailoring Lithium Deposition via an SEI‐Functionalized Membrane Derived from LiF Decorated Layered Carbon Structure

AbstractLithium (Li) metal is a key anode material for constructing next generation high energy density batteries. However, dendritic Li deposition and unstable solid electrolyte interphase (SEI) layers still prevent practical application of Li metal anodes. In this work, it is demonstrated that an uniform Li coating can be achieved in a lithium fluoride (LiF) decorated layered structure of stacked graphene (SG), leading to the formation of an SEI‐functionalized membrane that retards electron transfer by three orders of magnitude to avoid undesirable Li deposition on the top surface, and ameliorates Li+ ion migration to enable uniform and dendrite‐free Li deposition beneath such an interlayer. Surface chemistry analysis and density functional theory calculations demonstrate that these beneficial features arise from the formation of C–Fx surface components on the SG sheets during the Li coating process. Based on such an SEI‐functionalized membrane, stable cycling at high current densities up to 3 mA cm−2 and Li plating capacities up to 4 mAh cm−2 can be realized in LiPF6/carbonate electrolytes. This work elucidates the promising strategy of modifying Li plating behavior through the SEI‐functionalized carbon structure, with significantly improved cycling stability of rechargeable Li metal anodes.

29% P<sub>2</sub>O<sub>5</sub> Phosphoric Acid Desulphation: Improving the Performance of the Unit of Concentration

Clogging in the heat exchangers of the phosphoric acid concentration unit is a phenomenon which hinders the proper functioning of the installation. It results in the accumulation of undesirable solid deposits on the pipes and consequently a decrease of its performance. This deposit is mainly anhydrous or hemihydrate gypsum in addition to Na2SiF6. Phosphoric acid desulphation before its concentration step allows reducing this undesirable effect. Barium carbonate is used for the retention of sulphate ions using a simple experimental protocol which can easily be inserted into the phosphoric acid manufacturing. Four factors: quality of the phosphoric acid to be concentrated, amount of barium carbonate, temperature and time, were studied using design of experiment (DOE) methodology with two-level full factorial design strategy in order to assess their effects on desulphation. Only the first two factors have significant effects. Therefore, for effective sulphate removal, the validated statistical model (R2 = 99.96%) allows to predict the amount of barium carbonate to be used, depending on quality of the phosphoric acid to be concentrated and using the available temperature and time in the industrial process.

The use of membrane technologies in boiler houses of heat and power enterprises

The article is about the use of membrane technologies in water treatment cycle for boiler houses which use water of superficial reservoirs for operation. Working process of a flat membrane element is described in the article. Movement scheme of purified water streams is introduced. The layer of undesirable deposits which are slowing down membrane operation is formed on membrane surface during its operation. This formed layer is a result of the arising concentration polarization. Impact of low-frequency fluctuations on saturation water stream is offered to decrease concentration polarization which leads to decline in production of membrane devices. Fluctuations were brought in a stream by means of the vibrator. Steady standing waves are in the membrane device as a result of vibration effect. These waves reduce the formation of undesirable deposits layer on a membrane surface. Results received by mathematical modeling and confirmed by experimental studies state that process productivity of ultrafiltration increased by 30% in frequency range of 60-70 Hz. Frequency range is in standing wave.

EFFECTS OF THE USE OF D-LIMONENE AS AN ADDITIVE TO DIESEL-BIODIESEL BLENDS ON EXHAUST GASES COMPOSITION OF COMPRESSION IGNITION ENGINES

The transesterification of vegetable oils results in methyl esters of fatty acid, known as biodiesel. This one presents similar features of diesel oil, such as cetane number, specific weight, heat of combustion and air-fuel ratio. However, arising problems from its higher viscosity leads to a poor spraying by the fuel injectors and so to a low-grade combustion, causing formation of undesirable deposits inside the engine, changes in the properties of the lubricating oil and in the composition of the exhaust gas. Owing to this issue, it is necessary to study an additive able to make biodiesel characteristics more appropriate to be used in compression ignition engines, as well as a monitoring of changes in exhaust gas composition. The chosen additive was d-limonene, a monocyclic terpene obtained as a byproduct of citriculture. This paper presents the preliminary results obtained from the tests in a stationary diesel engine fuelled with mixtures of diesel-biodiesel and d-limonene, in different concentrations, comparing to regular diesel fuel. Although it was used in low concentrations, the additive was efficient in the reduction of hydrocarbons, carbon monoxide and opacity.

Development of a Miniaturized and Selective Impedance Sensor for Real-Time Slime Monitoring in Pipes and Tanks

A novel impedance sensor for monitoring the thickness of undesired micrometric deposits on the surfaces of water pipes and tanks is presented. Coplanar 10 μm-spaced gold microelectrodes were fouled in controlled laboratory conditions and the influence of slime on impedance response was measured. Two different sets of experiments were conducted to form slime on the electrodes surface, addressing biofilm growth and calcium carbonate precipitation, respectively. Following the formation, the thickness of the slime was characterized by Atomic Force Microscopy. Experimental tests highlighted that the impedance response is linear with to the thickness of the slime in both cases, in a 2 μm to 10 μm range. Interestingly, the slope of the response (i.e. of the ionic resistance change vs. thickness) is opposite: a decrease in the case of biofilm (-0.6 Ω/μm where the conductivity of the extracellular matrix becomes dominant) and an increase (+1.4 Ω/μm) in the case of inorganic deposits. In conclusion, this simple and robust sensor provides an accurate and selective determination of slime, while fouling and cleaning up cycles have demonstrated the possibility of regeneration. The final goal for the microsensor, once coupled to an electronic system for data processing and transmission, is the installation along the inner surface of pipes and tanks for real-time remote monitoring of long-term formation of slime with sub-micrometric thickness resolution.