Mass Transfer Research Articles

Polytriphenylamine Conjugated Microporous Polymers as Versatile Platforms for Tunable Hydrogen Storage.

Hydrogen (H2) as a fuel source presents a promising route toward decarbonization, though challenges in its storage remain significant. This study explores the synthesis and characterization of polytriphenylamine (PTPA)conjugated microporous polymers (CMPs) for H2 storage. Utilizing a combination of Buchwald-Hartwig (BH) coupling, the Bristol-Xi'an Jiaotong (BXJ) approach, and variations in monomer reactive site stoichiometry, a polymer with specific surface areas in excess of 1150 m2g-1 and micropore volume of 0.47cm3g-1 is developed. H2 storage capacities are measured, achieving excess gravimetric uptakes of 1.65 wt.% at 1bar and 2.51wt.% at 50bar and 77 K, with total capacities reaching 4.40 wt.% at 100bar and 77 K. Net adsorption isotherms reveal advantages to H2 storage using PTPA adsorbents over traditional compression up to pressures of 10bar at 77 K. High mass transfer coefficients of 4.95min-1 indicate a strong material affinity for H2. This study highlights the impact of monomer ratio adjustments on the porosity and excess, total, and net H2 adsorption capacities of PTPA-based CMPs, offering insights into the importance of a non-stoichiometric monomer concentration when developing efficient CMP-based H2 storage materials.

Laser-Regulated Iridium-Diffused Nitrogen-Carbon Sites for Enhanced Hydrazine-Assisted Alkaline Seawater Splitting and Zinc-Hydrazine Batteries.

The current study presents a quick and simple method for synthesizing Ir nanoclusters decorated on an N-doped carbon (NC) matrix via pulsed laser ablation in liquid, followed by pyrolysis. The resulting Ir-NC material acts as a dual-functional electrocatalyst, efficiently facilitating hydrogen generation through the hydrazine oxidation reaction (HzOR) and the hydrogen evolution reaction (HER) in alkaline seawater. The optimized Ir-NC-2 catalyst exhibits a low operating potential of 23mV versus the reversible hydrogen electrode for HzOR and a remarkably low overpotential of 24mV for HER, achieving a current density of 10mAcm-2 in alkaline seawater, surpassing the performance of the Pt/C catalyst. Notably, the Ir-NC-2 catalyst also demonstrates superior dual-functionality in overall hydrazine-assisted seawater splitting, requiring only 0.1V at 10mAcm-2 while maintaining stability. Moreover, density functional theory calculations reveal that the strong electronic interaction between the Ir nanoclusters and the NC matrix enhances mass transfer and electron conductivity, significantly boosting HER activity and accelerating the kinetics of hydrazine dehydrogenation. Consequently, the Ir-NC-2 catalyst performs efficiently in a Zn-hydrazine battery, achieving high energy efficiency of 95.5% and demonstrating excellent stability for 120h (360 cycles), indicating its potential for practical applications.

Boronize Coatings Studied with a New Mass Transfer Model.

This study examined the development of Fe2B (diiron boronize) coatings on the surface of 35NiCrMo4 steel through the thermochemical surface hardening process called boronizing. The morphology and thickness of the boronize coatings were assessed using Scanning Electron Microscopy (SEM) and optical microscopy (OM). A novel mathematical mass transfer model was developed to estimate the diffusion coefficients of boron in hard coating. The presence of uniformly distributed boronize coatings with a typical sawtooth pattern on the surface of the substrate was confirmed. The boronize coating's chemical composition and phase constituents were analyzed utilizing X-ray energy dispersive spectroscopy (EDS) and X-ray diffraction analysis (XRD). The study confirmed the presence of a single-phase boronize coating (Fe2B). Furthermore, microhardness tests indicated that the boronized specimen's surface demonstrated an average hardness of approximately 1953 HV. The wear study were conducted using the pin-on-disk method under dry debonding conditions at room temperature to estimate the coefficient of friction (COF) of the boronized (average ≈ 0.35) and untreated (0.725) specimens. The results revealed approximately 200% improvement in wear resistance due to the boronized coating. The empirical validation of the mathematical model was carried out for two additional boronizing conditions at 1223 K for 3 h and 1273 K for 1.5 h, resulting in an estimated percentage error of around 2.5% for both conditions. Additionally, an ANOVA analysis was performed, taking into account the temperature and time factors. The findings indicate that both factors exert a substantial influence on the dependent variable (u), with temperature (T) contributing 64.68%, time (t) contributing 27.37%, and the interaction of both factors (T × t) contributing 5.13%.

Исследование работы термической опреснительной установки с контактным испарителем и компрессией паровоздушной смеси

One of the global issues of our time is the shortage of freshwater resources. Desalination of marine and brackish waters is a promising solution to this problem. The most common desalination technologies are thermal (distillation) and baromembrane (reverse osmosis and nanofiltration) processes. When designing demineralization stations with reverse osmosis units, it is necessary to consider a number of limitations associated with higher requirements for pretreatment of water entering the unit. The use of thermal desalination plants makes it possible to obtain fresh water of higher quality, and less stringent requirements are imposed on the preliminary preparation of water for this type of unit. However, during the operation of desalination plants of this type, scale forms on the heating surfaces, which negatively affects the efficiency of the unit. Scale is formed less intensively in the units with contact vapors, since in this case the evaporation process occurs in volume. Thus, the development of thermal scheme of such unit and the study of their operation is relevant. The tasks have been solved using the methods of experimental studies of heat and mass transfer processes, mathematical processing of experimental data, and balance calculations of power plants. A thermal scheme of a thermal desalination plant with a contact evaporator with compression of a vapor-air mixture has been developed. Thermal and material balance has been compiled, on the basis of which energy costs have been determined to obtain m3 of fresh water. The authors have proved the determining influence of the temperature of desalinated water in the bubbling zone on the productivity of desalination plants with a contact evaporator. An amendment has been obtained that allows the initial salinity of water and brine to be considered when calculating the operating cycle of the unit. As a result of the analysis of the results obtained, it is found that an increase in the water temperature in the bubbling zone allows us to increase the productivity of the unit, and an increase of the drying temperature of the vapor-air mixture leads to a decrease of the energy consumption of the desalination plant. The introduction of an amendment considering the salinity of the source water and brine makes it possible to increase the accuracy of calculating air humidification up to 15 %.

Transport and competitive interfacial adsorption of PFOA and PFOS in unsaturated porous media: Experiments and modeling

Among emerging contaminants, per- and polyfluoroalkyl substances (PFAS) have captured public attention based upon their environmental ubiquity and potential risks to human health. Due to their typical surface release conditions and amphiphilic properties, PFAS tend to sorb to soil and accumulate at the air-water interface within the vadose zone. These processes can result in substantial plume attenuation. Although there is a growing body of literature on vadose zone transport, few studies have explored PFAS mixture transport, particularly under conditions where nonlinear sorption processes are important. The present study aims to advance our understanding of PFAS transport in variably saturated porous media through integration of experiments and mathematical modeling. Experiments include batch studies to quantify sorption to the solid phase, interfacial tension (IFT) measurements to estimate adsorption at the air-water interface (AWI), and column studies with F-70 Ottawa sand at 100 % and ca. 50 % water saturation to explore transport mechanisms. Employed PFAS solutions encompass individual solutes and binary mixtures of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) at concentration levels spanning four orders of magnitude to assess competitive and nonlinear sorption at the AWI. Observations demonstrate that concentration levels and competitive effects substantially influence PFAS transport in unsaturated systems. In the presence of PFOS, PFOA experienced less retention than would be anticipated based on single-solute behavior, and effluent breakthrough curves exhibited chromatographic peaking. The presented mathematical model for simultaneous flow and transport of PFAS was able to capture experimental observations with a consistent set of parameters and minimal curve fitting. These results demonstrate the robustness of the model formulation that included rate-limited interfacial mass transfer, an extended Langmuir-Szyszkowski model for adsorption at the AWI, and a scaled Leverett thermodynamic model to predict the AWI specific area. Overall, the results of this work underscore the importance of the AWI in PFAS transport and highlight the relevance of competition effects in adsorption formulations.

Interfacially Fabricated Covalent Organic Framework Membranes for Film-Based Fluorescence Humidity Sensors and Moisture Driven Actuators.

Rapid, on-site measurement of ppm-level humidity in real time remains a challenge. In this work, we fabricated a few micrometer thick, β-ketoenamine-linked covalent organic framework (COF) membrane via interfacially confined condensation of 1,3,5-tris-(4-aminophenyl)triazine (TTA) with 1,3,5-tri-formylphloroglucinol (TP). Based on the super-sensitive and reversible response of the COF membrane to water vapor, we developed a high-performance film-based fluorescence humidity sensor, depicting unprecedented detection limit of 0.005 ppm, fast response/recovery (2.2 s/2.0 s), and a detection range from 0.005 to 100 ppm. Remarkably, more than 7,000-time continuous tests showed no observable change in the performance of the sensor. The applicability of the sensor was verified by on-site and real-time monitoring of humidity in a glovebox. The superior performance of the sensor was ascribed to the highly porous structure and unique affinity of the COF membrane to water molecules as they enable fast mass transfer and efficient utilization of the water binding sites. Moreover, based on the remarkable moisture driven deformation of the COF membrane and its composition with the known polyimide films, some conceptual actuators were created. This study brings new ideas to the design of ultra-sensitive film-based fluorescent sensors (FFSs) and high-performance actuators.

Comprehensive study on copper adsorption using an innovative graphene carbonate sand composite adsorbent: Batch, fixed-bed columns, and CFD modeling insights

This study focused on an innovative graphene carbonate sand composite adsorbent, synthesized from carbonated porous sand and sucrose as raw materials, for the removal of copper ions via the adsorption process. The characteristics of this adsorbent are determined through comprehensive experiments and numerical simulations in batch and fixed-bed column conditions, which has not been extensively explored. Extensive experimentation demonstrated a remarkable 100 % removal efficiency under optimal conditions, which included a copper ion concentration of 3 g/L, a contact time of 10 h, and an adsorbent dosage of 35 g/L. The adsorption kinetics and isotherm results exhibited that the Elovich model (R² = 0.998) and the Langmuir model (R² = 0.996 for linear with qm=123.91 mg g-1, and R² = 0.993 for nonlinear fitting) more effectively described the adsorption of copper onto the adsorbent. In the fixed-bed column studies, among the well-known analytical models, the Log-Gompertz model showed better compatibility (R2 = 0.97∼0.99) between breakthrough curves with experimental results for various copper inlet concentrations. Also, numerical results obtained using computational fluid dynamics and mass transfer simulations with the linear driving force model were successfully validated by experimental results, particularly in the initial and transition zones of the breakthrough curve.

Hydrodynamic 3D Simulation of Roche Lobe Overflow in High-mass X-Ray Binaries

Abstract While binary merger events have been an active area of study in both simulations and observational work, the formation channels by which a high-mass star extends from Roche lobe overflow (RLO) in a decaying orbit of a black-hole (BH) companion to a binary black-hole (BBH) system merits further investigation. Variable length-scales must be employed to accurately represent the dynamical fluid transfer and morphological development of the primary star as it conforms to a diminishing Roche lobe under the runaway influence of the proximal BH. We have simulated and evolved binary mass flow under these conditions to better identify the key transitional processes from RLO to BBHs. We demonstrate a new methodology to model RLO systems to unprecedented resolution simultaneously across the envelope, donor wind, tidal stream, and accretion disk regimes without reliance upon previously universal symmetry, mass flux, and angular momentum flux assumptions. We have applied this method to the semidetached high-mass X-ray binary M33 X-7 in order to provide a direct comparison to recent observations of an RLO candidate system at two overflow states of overfilling factors f = 1.01 and f = 1.1. We found extreme overflow (f = 1.1) to be entirely conservative in both mass and angular momentum transport, forming a conical L1 tidal stream of density and deflected angle comparable to existing predictions. This case lies within the unstable mass transfer (MT) regime as recently proposed of M33 X-7. The f = 1.01 case differed in stream geometry, accretion disk size, and efficiency, demonstrating nonconservative stable MT through a ballistic uniform-width stream. The nonconservative and stable nature of the f = 1.01 case MT also suggests that existing assumptions of semidetached binaries undergoing RLO may mischaracterize their role and distribution as progenitors of BBHs and common envelopes.

Analytical Modeling of Mass and Heat Transfer on Unsteady Squeezing Viscous Nanofluid Flow under the Influence of Slip Velocity

In this article, two-dimensional unsteady incompressible viscous nanofluids magneto-hydrodynamic (MHD) flow among two parallel plates extended infinitely is investigated. The equations that results from the use of similarity transformations for non-linear partial differential system are solved by the new algorithm. The important key to this construct is the derivatives that appear as coefficients in the power series. The effects of apparent physical parameters on velocity concentration and temperature distributions are described using a schematic diagram and interpreted physically. The effects of apparent physical parameters on concentration, temperature, and velocity distributions are described by graphs. For the flow of nanofluids, the results indicate that it is inversely proportional between the rate of mass and heat transfer with nanoparticle size fraction and magnetic parameter. Over time, squeeze number and schmidt number lead to increase the rate of mass transfer. This problem is dissolved numerically by using the Runge-Kutta scheme of fourth-order (RK4S) .

Enhancing Hydrogen Evolution Reaction through the Improved Mass Transfer and Charge Transfer by Bimetal Nodes.

The high cost of hydrogen production by water electrolysis severely challenges its commercial application. It is highly desirable to develop efficient electrocatalysts and innovative electrolytic cells. Introducing additional metal nodes to form bimetallic metal-organic framework (MOF) is a simple, feasible strategy to overcome the poor electrocatalytic performance of single-metal MOF. In this study, the hydrothermal method is used to synthesize bimetallic NixCoy-BTC. It is found that for hydrogen evolution reaction (HER), Ni0.8Co0.2-BTC merely requires a potential of -0.203 V (vs reverse hydrogen electrode, RHE) to achieve 10 mA cm-2, which is significantly lower than that of Ni-BTC (-0.341 V vs RHE). Notably, electrochemical impedance spectroscopy (EIS) and distribution of relaxation time (DRT) analysis indicate that NixCoy-BTC has improved charge transfer and mass transfer process, compared with Ni-BTC. Electron paramagnetic resonance (EPR) confirms that Ni0.8Co0.2-BTC has more unpaired electrons than Ni-BTC. Density functional theory (DFT) calculations show that compared with Ni-BTC, NixCoy-BTC is more thermodynamically favorable for the adsorption of H+, OH-, and H2O. It demonstrates that the change of mass transfer caused by bimetallic nodes and the delicate variation of MOF surface play an important role in the electrochemical process. Moreover, a novel electrolytic cell was developed using a methanol oxidation reaction (MOR) to replace oxygen evolution reaction (OER). In this MOR-based electrolytic cell, a current density of 50 mA cm-2 can be achieved at only a cell voltage of 1.85 V, which is lower than the 2.22 V of OER-based electrolytic cell, suggesting that 16.7% electric energy can be saved. At the same time, the Faraday efficiency (FE, 98.2%) of the MOR-based cell is higher than that (94.5%) of the OER-based cell. This research offers a promising strategy for low-cost hydrogen production.

Numerical Assessment of MHD Tri-Hybrid Nanoparticles by Tangent Hyperbolic Model with Chemical Reaction: Thermodynamic Analysis

This paper investigates the influence of magneto-tangent hyperbolic nanofluid on the flow of a tri-hybrid nanoliquid consisting of [Formula: see text], and [Formula: see text] particles suspended in [Formula: see text]. The entropy production is encountered in this analysis. The fluid flows over a stretch sheet is considered. In addition, the energy equation also assumes the existence of a uniform heat source or sink and thermal radiation. Furthermore, the concentration equation emphasizes the chemical reaction. The current proposed model yields a set of nonlinear governing equations. The modeled formulation is transformed into a dimensionless system through the application of a suitable alteration. The complex nonlinear equation system was solved using the bvp4c through numerical methods. The main motive of this exploration is to emphasize the rate of heat and mass transfer in a flow of [Formula: see text], and [Formula: see text]-based hybrid nanofluid across a stretch sheet. The graphical study illustrates that Weissenberg number and magnetic field enhancement result in decreasing the velocity. But thermal layer, entropy production, and Bejan number are enhanced with larger values of Weissenberg number and magnetic field. This study focuses on different profiles with various flow parameters. Furthermore, we have compared the tri-hybrid nanofluid with the hybrid and mono nanofluid in all the figures and tabular format. Additionally, we have compared tri-hybrid, hybrid, and mono nanofluid using graphs for velocity, temperature, concentration, entropy production, and Bejan number.

Pros and cons of airlift and bubble column bioreactors: How internals improve performance

Gas fermentation is a promising technology of high commercial interest, particularly for capturing CO2 and CO from industrial off-gases to reduce greenhouse gas emissions and replace fossil fuels for bulk chemical production. Therefore, evaluating promising bioreactor settings ab initio is a crucial step. Whereas alternate configurations may be tested in laborious scale up studies, the procedure may be accelerated by in silico studies that accompany or even partially replace wet-lab work once the models are validated. In this context, the current study compares various pneumatically agitated reactor types – bubble column reactor (BCR), annulus- and center-rising internal-loop airlift reactor (AR-IL-ALR and CR-IL-ALR), and external-loop airlift reactor (EL-ALR) – to identify advantages and disadvantages for the given application based on computational fluid dynamics (CFD) models. Process performance is optimized by introducing internal structures to guide the flow. Despite a significant increase in the mass transfer coefficient (kLa) through internal modifications, the CR-IL-ALR still exhibited the poorest performance. The optimized AR-IL-ALR demonstrated good mixing and, after introducing an open-cone shaped internal in the head part and a conical bottom, superior mass transfer, achieving an enhancement over 10 % in the mass transfer coefficient to 315 1/h. This study thereby outlines the potential of internal structures for process improvement, as well as the value of a priori in silico design of reactor configurations.

A modeling method based on incomplete mixed cells in counter-current chromatography: Interphase mass transfer ratio

Complex mass transfer processes are highly involved in the performance of counter-current chromatography (CCC), so profound exploration should be conducted to improve the overall performance. To more accurately estimate the interphase mass transfer efficiency in the elution process, this study proposes an incomplete mixed cell model by linking layering-mixing-layering behavior and wave-like mixing. With the model, we proposed a fast estimation algorithm for interphase mass transfer ratio (IMTR), which can independently reflect the magnitude of the interphase mass transfer efficiency. The experimental results show that the IMTR of all samples was relatively small, with an average value of not >10 % under different operating conditions. This indicates that the low column efficiency of CCC may be mainly due to the low efficiency of interphase mass transfer. In addition, by analyzing the influencing factors of IMTR, it is found that IMTR is positively correlated with the number of theoretical plates and the retention of stationary phase (Sf), but negatively correlated with the number of incomplete mixing cells (n). Therefore, in the study of column efficiency optimization, we recommend that the distribution ratio, Sf, and n should remain unchanged in control experiments to ensure that IMTR directly reflects the effect on interphase mass transfer efficiency. This study further completes the evaluation index of the CCC column efficiency, revealing the underlying mechanisms of IMTR on column efficiency and providing a theoretical foundation for future research on high-efficiency CCC.

Hydrogen Yield Enhancement in Biogas Dry Reforming with a Ni/Cr Catalyst: A Numerical Study

This numerical study investigates the impact of the reaction temperature, molar ratio of CH4:CO2, and catalyst porosity (εp) on the H2 yield and H2 selectivity during biogas dry reforming over a Ni/Cr catalyst. Using COMSOL Multiphysics, we conducted detailed simulations to elucidate the underlying reaction characteristics. Our findings reveal that increasing εp from 0.1 to 0.95 significantly provides a 5 times increase in H2 production and a 2.3% increase in H2 selectivity while simultaneously reducing CO selectivity by 2.3%. This effect is attributed to the improved mass transfer within the catalyst bed, leading to more efficient reactant conversion and product formation. Additionally, we observed a strong correlation between higher reaction temperatures and increased H2 yield and H2 selectivity. By optimizing these operational parameters, our results suggest that Ni/Cr catalysts can be effectively employed for the sustainable production of H2 from biogas.

Hierarchical core-shell ZIF-11@ZIF-8 composite nanocatalyst for high-yield simultaneous transesterification-esterifications of sunflower oil to produce biodiesel

Decreasing the mass transfer resistance is a promising technique to prepare an efficient catalyst for improving biomass macromolecules conversion in biodiesel production. In this study, hierarchical core–shell composite nanocatalysts were prepared through a solvothermal technique using zeolitic imidazolate framework-8 (ZIF-8) and ZIF-11 metal–organic frameworks (MOFs). The nanocatalysts were characterized by XRD, FT-IR, BET, FE-SEM, EDS, XPS, TEM, NH3-TPD, and CO2-TPD analyses. The results showed high crystallinity, high surface area (1446.86 m2/g), high pore volume (0.65 cm3 g−1), and mesoscale pore size (2.37 nm). Furthermore, TEM images confirmed the formation of core–shell structure for the composites. The catalytic activity was evaluated in the transesterification of sunflower oil at different operating conditions. The highest biodiesel yield (96.4 %) and full free fatty acid (FFA) conversion were obtained over the ZIF-11@ZIF-8 nanocatalyst at the optimum operating conditions: 120 °C, catalyst concentration of 8 wt%, methanol to oil ratio of 40:1, and 10 h. The ZIF-11@ZIF-8 nanocatalyst showed high thermal and chemical stability after several sequence cycles, leading to high reusability.

Novel ellipsoid-like granules exhibit enhanced anammox performance compared to sphere-like granules

Anammox granular sludge (AnGS) serves as an important platform for cost-effective nitrogen removal from wastewater. Different to the traditionally sphere-like granules, a novel type of AnGS in a unique ellipsoid-like shape was obtained through enhancing shear force. The ellipsoid-like AnGS significantly exhibited a smaller aspect ratio (-25.1 %) and granular size (-11.8 %), compared to traditional sphere-like AnGS (p < 0.01). Comprehensive comparisons showed that ellipsoid-like AnGS possessed a significantly higher extracellular polymeric substances (EPS) content and strength, as well as an enhanced mass transfer and a higher viable bacteria proportion due to the larger substrate permeable zone (p < 0.01). Additionally, the anammox bacterial abundance (Candidatus Kuenenia) was 12.2 % higher in ellipsoid-like AnGS than in sphere-like AnGS. All these characteristics of ellipsoid-like AnGS jointly increased the specific anammox activity by 29.0 % and nitrogen removal capacity by 22.6 %, compared to sphere-like AnGS. Further fluid field simulation suggested the enhanced flow shear on the side surface of AnGS likely drove the formation of ellipsoid-like AnGS. The higher shear force on the side surface led to an increase of EPS content (especially hydrophobic protein) and elastic modulus, thus constraining lateral expansion. This study sheds light on impacts of granular shape, an overlooked morphological factor, on anammox performance. The ellipsoid-like AnGS presented herein also offers a unique and promising aggregate to enhance anammox performance.

A Simulation Study on the Effect of Supersonic Ultrasonic Acoustic Streaming on Solidification Dendrite Growth Behavior During Laser Cladding Based on Boundary Coupling

Laser cladding has unique technical advantages, such as precise heat input control, excellent coating properties, and local selective cladding for complex shape parts, which is a vital branch of surface engineering. During the laser cladding process, the parts are subjected to extreme thermal gradients, leading to the formation of micro-defects such as cracks, pores, and segregation. These defects compromise the serviceability of the components. Ultrasonic vibration can produce thermal, mechanical, cavitation, and acoustic flow effects in the melt pool, which can comprehensively affect the formation and evolution for the microstructure of the melt pool and reduce the microscopic defects of the cladding layer. In this paper, the coupling model of temperature and flow field for the laser cladding of 45 steel 316L was established. The transient evolution laws of temperature and flow field under ultrasonic vibration were revealed from a macroscopic point of view. Based on the phase field method, a numerical model of dendrite growth during laser cladding solidification under ultrasonic vibration was established. The mechanism of the effect of ultrasonic vibration on the solidification dendrite growth during laser cladding was revealed on a mesoscopic scale. Based on the microstructure evolution model of the paste region in the scanning direction of the cladding pool, the effects of a static flow field and acoustic flow on dendrite growth were investigated. The results show that the melt flow changes the heat and mass transfer behaviors at the solidification interface, concurrently changing the dendrites’ growth morphology. The acoustic streaming effect increases the flow velocity of the melt pool, which increases the tilt angle of the dendrites to the flow-on side and promotes the growth of secondary dendrite arms on the flow-on side. It improves the solute distribution in the melt pool and reduces elemental segregation.

On Assessing a Potential Reuse of the Indonesian Post-Operation Offshore Oil/Gas Pipelines as A Cold-Water Pipe for an Ocean Thermal Energy Conversion (OTEC) System: A Thermal and Fluid Dynamic Perspective

One of the main issues arising in offshore oil and gas decommissioning is associated with significant required costs. Research assessing the potential reuse of the post-operation offshore oil and gas pipeline (POGP) in Indonesia for the Ocean Thermal Energy Conversion (OTEC) system offer double the potential cost reductions in POGP decommissioning and OTEC development. In the context of OTEC development, research on increasing system efficiency makes a significant effort by modifying working fluids and usually by employing the assumption that the temperature of the cold seawater at the surface outlet of the Cold-Water Pipe (CWP) is practically the same as that at the inlet of the CWP at a depth of about 900 m. Unfortunately, this was not the case when the POGP was to be reused for the OTEC system because there was difficulty in applying additional insulation to the existing subsea pipelines. The temperature change in the cold seawater is even more critical considering that oil and gas operations at a depth of 900 m could be associated with more than 60 km of pipeline length to reach an onshore system for a typical seabed bathymetry. This paper assesses the potential reuse of the POGP as a CWP for the Ocean OTEC system. The temperature distribution within CWP is analyzed using a thermal and fluid dynamics approach. The results show that the reuse of POGP for the OTEC system could offer an excellent opportunity for capital cost reductions because the POGP has a remaining service life of over 20 years. However, the results of the analysis of heat and mass transfers show that the temperature change in cold seawater at CWP is about 3 to 6 oC, depending on the technical scenarios of the pipelines. The POGP used in the OTEC system could be suitable for a 20 kW OTEC system with practically no cost of pipelines, which usually accounts for a significant investment cost.

Immobilization of Coupled Enzymes onto Metalated Hierarchical Organic Microspheres.

Hierarchical organic microspheres (HOMs) have emerged as an ideal carrier for immobilizing biomacromolecules. In this research, an in-depth investigation into the structural characteristics of a striated HOM, known as HOM-15, has revealed the assembly mechanism of microspheres through weakly stacked two-dimensional structural units that are composed of V-shaped small organic molecules. With the leverage of this understanding, HOM-15 was adopted as a stable and reusable platform for co-immobilizing of ene-reductases and glucose dehydrogenases via metal ion bridging onto the surface of HOMs. The research demonstrates that metal ion bridging can finely tune the surface properties of HOM-15, thereby facilitating the immobilization of enzymes that would otherwise be impeded by electrostatic repulsion. Comparing HOM-15 to other microspherical variants revealed its superior biocatalytic performance, attributed to the reduction of the mass transfer barrier facilitated by its lamellar-stacking morphology. This novel biocatalytic system underscores the potential applications of HOMs in broader biocatalytic processes.

Relationships of ternary activities for the enhanced Cr(VI) removal by coupling nanoscale zerovalent iron with sulfidation and carboxymethyl cellulose

Nanoscale zerovalent iron (nZVI) has been extensively applied in water pollution control. However, the reactivity of nZVI toward contaminants is mainly limited by its corrosion and agglomeration. In this study, the nZVI modified by sulfidation coupled with carboxymethyl cellulose (CMC) (C-S-nZVI) was synthesized and characterized by TEM and electrochemical techniques. Taking Cr(VI) as the contaminant, it was found that the sulfidation could couple with CMC modification to not only enhance the reactivity of nZVI toward Cr(VI), but also regulate the sedimentation activity and corrosion activity of nZVI in water. Particularly, the optimal kobs (0.0816 min−1) obtained by the C-S-nZVIone-0.16 (i.e., one-step sulfidation and its S/Fe molar ratio was 0.16) was approximately 27.2 times higher than that by the nZVI (0.0030 min−1). Moreover, based on the correlation analysis of the ternary activities, this study confirmed that the reactivity of C-S-nZVI toward Cr(VI) was negatively correlated with its sedimentation activity (slope = −0.7623, R = 0.59) and corrosion activity (slope = −0.0171, R = 0.56), respectively. XPS and TEM results further revealed that CMC could couple with iron sulfides (FeSx) to enhance the mass transfer of Cr(VI) toward nZVI and subsequent electron transfer from Fe0 core to out, ultimately improving the reduction of Cr(VI) by nZVI. Overall, this study introduced a new evaluation method based on the ternary activity of nZVI, providing theoretical support for the practical application of nZVI-based technology.