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Benchtop NMR analysis combined with model-based fitting protocols can detect commercial honey adulteration down to 5 wt%.

SUMMARY The use of nuclear magnetic resonance (NMR) techniques allows in situ characterization of geophysical properties such as moisture content, permeability and wettability. However, the accuracy and applicability of such measurements is limited by internal magnetic field gradients which are a consequence of magnetic susceptibility differences at solid–fluid interfaces. Such effects are particularly prominent in iron ore rock samples which contain ferrimagnetic and ferromagnetic mineralogy leading to high magnetic susceptibility. Multiple echo time Carr–Purcell–Meiboom–Gill (CPMG) NMR pulse sequences are commonly used to capture the influence of internal gradients, with the intention of deconvoluting diffusion in effective internal gradients (geff) from true transver relaxation (T2). The interpretation of such measurements is complicated by the presence of multiple diffusive regimes: the short-time (ST), motionally averaged and localization regimes respectively. We introduce a new model for diffusive NMR signal attenuation, called the multiregime model which is intended to better capture diffusive behaviour across the three regimes. The multiregime model is compared against previous methods for quantifying diffusive decay (the ST only and generalized inversion models). Multi-echo measurements of iron ore samples are fit with each model in order to quantify 2-D T2–geff distributions. The resulting distributions demonstrate how the multiregime model can provide insight into the relative influence of the different diffusive regimes in a given sample. This assists in understanding the influence of diffusive decay on measurement accuracy, for example the increased measurement error with increasing prevalence of the localization regime. The multiregime model provides a key step in accurately segregating surface relaxation and diffusive relaxation, which is crucial for accurately estimating pore size distributions, permeability and wettability in high magnetic susceptibility samples using NMR.

Simulations of nuclear magnetic resonance (NMR) signal from fluids contained in porous media (such as rock cores) need to account for both enhanced surface relaxation and the presence of internal magnetic field gradients due to magnetic susceptibility contrast between the rock matrix and the contained fluid phase. Such simulations are typically focussed on the extraction of the NMR T2 relaxation distribution which can be related to pore size and indirectly to system permeability. Discrepancies between such NMR signal simulations on digital rock cores and associated experimental measurements are however frequently reported; these are generally attributed to spatial variations in rock matric composition resulting in heterogeneously distributed NMR surface relaxivities (ρ) and internal magnetic field gradients. To this end, a range of synthetic sediments composed of variable mixtures of quartz and garnet sands were studied. These two constituents were selected for the following reasons: they have different densities allowing for ready phase differentiation in 3D μCT images of samples to use as simulation lattices and they have distinctly different ρ and magnetic susceptibility values which allow for a rigorous test of NMR simulations. Here these 3D simulations were used to calculate the distribution of internal magnetic field gradients in the range of samples, these data were then compared against corresponding NMR experimental measurements. Agreement was reasonably good with the largest discrepancy being the simulation predicting weak internal gradients (in the vicinity of the quartz sand for mixed samples) which were not detected experimentally. The suite of 3D μCT images and associated experimental NMR measurements are all publicly available for the development and validation of NMR simulation efforts.

Growing interest in liquefied natural gas (LNG) as a rocket fuel demands reliable prediction and an improved understanding of the changes in its composition arising from the preferential boil-off of lighter components during long duration storage. Unfortunately, current methods of predicting boil-off gas (BOG) evolution from cryogenic liquids are based on limited experimental data. This work reports a series of new experiments which measure the temporal change in BOG production, composition, and pressure at industrially relevant conditions for both ternary mixtures of methane, ethane, and nitrogen and an LNG mixture used as rocket fuel. Faster pressure build-up rates are consistently observed with decreasing initial liquid volume fraction, whilst a decline of 8% in the LNG higher heating value was observed after thirty-three days of weathering. The data is compared with a robust and efficient superheated vapor (SHV) model, implemented in the software package BoilFAST, which allows for reliable calculations of self-pressurisation and boil-off losses for different tank geometries and thermal insulation systems. The model exhibits good agreement with the experimental data across all conditions explored. Finally, the potential effect of LNG composition and heating value changes on rocket engine performance was assessed by examining changes in the adiabatic flame temperature and burnt gas volume ratio. While our data suggest that the rocket engine performance would improve as a result of weathering, the effectiveness of the weathered LNG as a coolant in a regeneratively cooled rocket engine decreases.

SummaryMultiphase flowmetering is a requirement across a range of process industries, particularly those that pertain to oil and gas. Generally, both the composition and individual phase velocities are required; this results in a complex measurement task made more acute by the prevalence of turbulent flow and a variety of flow regimes. In the current review, the main technical options to meet this metrology are outlined and used to provide context for the main focus on the use of nuclear magnetic resonance (NMR) technology for multiphase flowmetering. Relevant fundamentals of NMR are detailed as is their exploitation to quantify flow composition and individual phase velocities for multiphase flow. The review then proceeds to detail three NMR multiphase flowmeter (MPFM) apparatus and concludes with a consideration of future challenges and prospects for the technology.

Hydrogen is emerging as one of the most promising energy carriers for a decarbonised global energy system. Transportation and storage of hydrogen are critical to its large-scale adoption and to these ends liquid hydrogen is being widely considered. The liquefaction and storage processes must, however, be both safe and efficient for liquid hydrogen to be viable as an energy carrier. Identifying the most promising liquefaction processes and associated transport and storage technologies is therefore crucial; these need to be considered in terms of a range of interconnected parameters ranging from energy consumption and appropriate materials usage to considerations of unique liquid-hydrogen physics (in the form of ortho–para hydrogen conversion) and boil-off gas handling. This study presents the current state of liquid hydrogen technology across the entire value chain whilst detailing both the relevant underpinning science (e.g. the quantum behaviour of hydrogen at cryogenic temperatures) and current liquefaction process routes including relevant unit operation design and efficiency. Cognisant of the challenges associated with a projected hydrogen liquefaction plant capacity scale-up from the current 32 tonnes per day to greater than 100 tonnes per day to meet projected hydrogen demand, this study also reflects on the next-generation of liquid-hydrogen technologies and the scientific research and development priorities needed to enable them.

In subsea oil and gas production, a transition away from complete gas hydrate avoidance to risk-based hydrate management has the potential to offer cost savings and improved viability for new devel...

The production of methane (CH4) from natural-gas hydrate deposits via molecular replacement by injected, thermodynamically more favourable, carbon dioxide (CO2) is a promising method of energy prod...

We demonstrate an unexpected decay-recovery behaviour in the time-dependent $^{1}\mathrm{H}$ NMR relaxation times of water confined within a hydrating porous material. Our observations are rationalised by considering the combined effects of decreasing material pore size and evolving interfacial chemistry, which facilitate a transition between surface-limited and diffusion-limited relaxation regimes. Such behaviour necessitates the realisation of temporally evolving surface relaxivity, highlighting potential caveats in the classical interpretation of NMR relaxation data obtained from complex porous systems., Comment: 12 pages, 2 figures

In this study non-invasive low field magnetic resonance imaging (MRI) technology was used to monitor fouling induced changes in fiber-by-fiber hydrodynamics inside a multi-fiber hollow fiber membrane module containing 401 fibers. Using structural and velocity images the fouling evolution of these membrane modules were shown to exhibit distinct trends in fiber-by-fiber volumetric flow, with increasing fouling causing a decrease in the number of flow active fibers. This study shows that the fouling rate is not evenly distributed over the parallel fibers, which results in a broadening of the fiber to fiber flowrate distribution. During cleaning, this distribution is initially broadened further, as relatively clean fibers are cleaned more rapidly compared to clogged fibers. By tracking the volumetric flow rate of individual fibers inside the modules during the fouling-cleaning cycle it was possible to observe a fouling memory-like effect with residual fouling occurring preferentially at the outer edge of the fiber bundle during repeated fouling-cleaning cycle. These results demonstrate the ability of MRI velocity imaging to quantitatively monitor these effects which are important when testing the effectiveness of cleaning protocols due to the long term effect that residual fouling and memory-like effect may have on the operation of membrane modules.

Understanding the behaviour of short-chain hydrocarbons confined to porous solids informs the targeted extraction of natural resources from geological features, and underpins rational developments in separation, storage and catalytic conversion processes. Herein, we report the application of low-field (12.7 MHz)

Solid-fluid interactions underpin the efficacy of functional porous materials across a diverse array of chemical reaction and separation processes. However, detailed characterization of interfacial phenomena within such systems is hampered by their optically opaque nature. Motivated by the need to bridge this capability gap, we report low-magnetic-field two-dimensional (2D) 1H nuclear spin relaxation measurements as a noninvasive probe of adsorbate identity and interfacial dynamics, exploring the relaxation characteristics exhibited by liquid hydrocarbon adsorbates confined to a model mesoporous silica. For the first time, we demonstrate the capacity of this approach in distinguishing functional group-specific relaxation phenomena across a diverse range of alcohols and carboxylic acids employed as solvents, reagents, and liquid hydrogen carriers, with distinct relaxation responses assigned to the alkyl and hydroxyl moieties of each confined liquid. Uniquely, this relaxation behavior is shown to correlate with adsorbate acidity, with the observed relationship rationalized on the basis of surface-adsorbate proton-exchange dynamics. Our results demonstrate that nuclear spin relaxation provides a molecular-level perspective on sorbent/sorbate interactions, motivating the exploration of such measurements as a unique probe of adsorbate identity within optically opaque porous media.

The application of membrane technology for water treatment and reuse is hampered by the development of a microbial biofilm. Biofilm growth in micro-and ultrafiltration (MF/UF) membrane modules, on both the membrane surface and feed spacer, can form a secondary membrane and exert resistance to permeation and crossflow, increasing energy demand and decreasing permeate quantity and quality. In recent years, exhaustive efforts were made to understand the chemical, structural and hydraulic characteristics of membrane biofilms. In this review, we critically assess which specific structural features of membrane biofilms exert resistance to forced water passage in MF/UF membranes systems applied to water and wastewater treatment, and how biofilm physical structure can be engineered by process operation to impose less hydraulic resistance (“below-the-pain threshold”). Counter-intuitively, biofilms with greater thickness do not always cause a higher hydraulic resistance than thinner biofilms. Dense biofilms, however, had consistently higher hydraulic resistances compared to less dense biofilms. The mechanism by which density exerts hydraulic resistance is reported in the literature to be dependant on the biofilms’ internal packing structure and EPS chemical composition (e.g., porosity, polymer concentration). Current reports of internal porosity in membrane biofilms are not supported by adequate experimental evidence or by a reliable methodology, limiting a unified understanding of biofilm internal structure. Identifying the dependency of hydraulic resistance on biofilm density invites efforts to control the hydraulic resistance of membrane biofilms by engineering internal biofilm structure. Regulation of biofilm internal structure is possible by alteration of key determinants such as feed water nutrient composition/concentration, hydraulic shear stress and resistance and can engineer biofilm structural development to decrease density and therein hydraulic resistance. Future efforts should seek to determine the extent to which the concept of “biofilm engineering” can be extended to other biofilm parameters such as mechanical stability and the implication for biofilm control/removal in engineered water systems (e.g., pipelines and/or, cooling towers) susceptible to biofouling.

Understanding solid-fluid interactions within porous materials is critical for their efficient utilisation across chemical reaction and separation processes. However, detailed characterisation of interfacial phenomena within such systems is hampered by their optically opaque nature. Motivated by the need to bridge this capability gap, we detail here the application of low magnetic field 2D 1H nuclear spin relaxation measurements as a non-invasive probe of sorbate/sorbent interactions, exploring the relaxation characteristics exhibited by liquid adsorbates confined to a model mesoporous silica. For the first time, we demonstrate the capacity of such measurements to distinguish functional group-specific relaxation phenomena across a diverse range of protic adsorbates of wide importance as solvents, reagents, and hydrogen carriers, with distinct relaxation environments assigned to the alkyl and hydroxyl moieties of the confined liquids. Uniquely, this relaxation behaviour is shown to correlate with adsorbate acidity, with the observed relationship rationalised on the basis of surface-adsorbate proton exchange dynamics.

Tortuosity is an important physical characteristic of porous materials; for example, it is a critical parameter determining the effective diffusion coefficient dictating mixing between miscible fluids in porous rock structures as is relevant to enhanced gas recovery processes. Accurate measurement of tortuosity remains challenging, resulting in various definitions dictated largely by the measurement protocol applied. Here, we focus primarily on ‘diffusive’ tortuosity (τd), which is defined as the ratio of the bulk fluid diffusion coefficient to the restricted diffusion coefficient applicable to the porous media under study. Specifically, we consider carbonate rock cores ranging in permeability from 2 to 5300 mD and adapt pulsed field gradient (PFG) NMR methodology such that accurate measurements of tortuosity are obtained over a sufficiently representative length scale of the porous media. To this end, we deploy supercritical methane as a probe molecule exploiting both its high mobility and proton density. Tortuosity measurements are shown to be independent of both pressure and diffusion observation time, conclusively proving that our measurements are in the asymptotic regime in which all of the pore space is adequately sampled by the diffusing methane molecules. The resultant ‘diffusive’ tortuosity measurements (which ranged from 3.1 to 5.6) are then compared against independent electrical conductivity measurements of tortuosity using a two-electrode impedance technique applied to the carbonate samples saturated with brine solution. Agreement between the ‘diffusive tortuosity,’ as measured by PFG NMR, and ‘electrical’ tortuosity was remarkably good (within 10%), given the very different measurements techniques used, for most of the carbonate rock samples considered.

Asphaltenes are widely associated with the unwanted stability of water-in-crude oil (w/o) emulsions due to their inhibitory effect on water droplet coalescence. Here, we seek to prove that certain crude oil resins that can bind with asphaltenes, hereafter referred to as binding resins, are capable of solvating these asphaltenes such that the w/o emulsion destabilizes. W/o emulsions were formed using a variety of crude oils as well as model oils with varying amounts of resins and asphaltenes. A modified SARA fractionation technique was adopted to extract the required resins and asphaltenes. Emulsion stability was tracked over time both visually and via the use of pulsed field gradient nuclear magnetic resonance to quantify the emulsions’ water droplet size distributions. It was conclusively found that the binding resins significantly improved the demulsification rate of the emulsions formed using both crude oil and model oils. In the case of the model oils, this influence could only be attributed to the re...

We present a novel multiphase flow metering technique for simultaneous measurement of oil and water volumetric flowrates. An Earth’s field nuclear magnetic resonance (NMR) detection coil is applied to measure free induction decay (FID) signals of two-phase oil/water flows. A dual polarisation technique is introduced utilising an upstream permanent magnet as well as an electromagnetic pre-polarising coil. FID signals with variable pre-polarising conditions are acquired and fit with a model for the NMR fluid signal using a 2D Tikhonov regularisation algorithm, allowing determination of a joint 2D velocity-T1 probability distribution. Appropriate analysis of the measured velocity-T1 distributions allows calculation of individual phase flowrates. The performance of the NMR flow measurement technique is examined for oil/water flows which are visually observed to be in three different flow regimes: stratified flow with mixing, dispersion of oil-in-water and water, and full oil-in-water emulsions. Two-phase flow characteristic features such as velocity slip are examined for each flow regime. Finally the accuracy of the measurement system in each flow regime is validated against in-line rotameter measurements.

Under high-pressure and low-temperature conditions, gas hydrate shells may form and grow at the interface of water droplets in water-in-oil emulsions. Such hydrate formation can enable downstream agglomeration and slurry viscosification, thus increasing the risk of hydrate blockage. Therefore, emulsion stability represents a critical parameter in understanding this overall flow behaviour. In this study, the impact of three common and widely-used industrial anti-agglomerants from three different suppliers (AA-1, AA-2 and AA-3—exact composition is commercially sensitive) on 30 wt% water-in-oil (W/O) emulsion stability was investigated. Bench-top nuclear magnetic resonance (NMR) pulsed field gradient (PFG) methods were used to measure the droplet size distributions (DSDs) of the W/O emulsions as a complement to bottle stability test. In the absence of hydrate anti-agglomerants, based on visual observation, 85% of the original W/O emulsion remained after 10 h. In the presence of AA-1 and AA-2, 94% of the original emulsion was retained; in contrast, AA-3 acted to destabilise the emulsion with only 64% of the original emulsion visually evident after 10 h. These results were substantiated by PFG NMR measurements which showed substantial changes in droplet size as a function of sample height for the W/O emulsion formulated with AA-3. Interestingly the W/O emulsion formulated with AA-1, while very stable, was characterised by comparatively very large water droplets, indicative of a complex multiple water-in-oil-in-water (W/O/W) emulsion microstructure. AA-2 forms stable emulsion with small droplets of water dispersed in the oil phase. Our results provide insight into a wide range of potential impacts of AA addition on an industrial crude oil pipeline, in which AA-1 resulted in a complex W/O/W multiple emulsion, AA-2 behaved as an emulsifier and AA-3 behaved as a demulsifier.

The production of water during crude oil extraction may result in the formation of stable water-in-oil emulsions. Such emulsions are problematic for a variety of reasons; for example, they increase the fluid viscosity and hence the pumping costs. Previously, Ling; [NMR Studies of the Effect of CO2 on Oilfield Emulsion Stability. Energy Fuels 2016, 307, 5555–5562] have shown that treating these water-in-crude oil emulsions with subcritical CO2 at 50 bar can lead to their breakage. These measurements utilized benchtop NMR pulsed field gradient (PFG) techniques to monitor the evolution in the emulsion droplet size distribution, which is a precursor to emulsion breakage. Experimental limitations meant, however, that the measurements were performed only following depressurization of the applied CO2 and as such were unable to directly distinguish between two potential mechanisms for emulsion breakage as proposed in the literature: (i) CO2 bubble formation within the water droplets upon depressurization or (ii) ...

Injection of carbon dioxide (CO2) into a natural gas reservoir is an emerging technology for enhanced natural gas recovery (EGR) realizing increased natural gas production whilst sequestering the injected CO2. However, given that CO2 and natural gas are completely miscible, simulation of potential EGR scenarios is required to determine when breakthrough of CO2 will occur at the natural gas production wells. For such reservoir simulations to be reliable (independent of software used), accurate dispersion data between CO2 and natural gas at relevant reservoir conditions are required. To this end, we apply one-dimensional magnetic resonance imaging (MRI) to quantify this dispersion process in situ in both sandstone and carbonate rock cores. Specifically we apply the SPRITE MRI sequence (Balcom et al. in J Magn Reson Ser A 123(1):131–134, 1996. https://doi.org/10.1006/jmra.1996.0225 ) to facilitate quantitative axial profiles of methane (CH4) content during core flooding processes between CO2 and CH4. Simultaneously we measure, using infrared, the effluent CO2 and CH4 concentrations enabling ex situ dispersion measurements. Via comparison with the corresponding MRI data, the erroneous contributions to dispersion from entry/exit effects and mixing in piping to and from the rock core holder are quantified. Furthermore, we demonstrate how nuclear magnetic resonance T2 measurements can be uniquely used to probe the pore size occupancy of the CH4 during the core flooding process.

The emergence and accumulation of microplastics (MPs) in various aquatic environments have recently raised significant concerns. Wastewater treatment plants (WWTPs) have been identified as one of the major sources of MPs discharge to the environment, implying a substantial need to improve advanced techniques for more efficient removal of MPs. Polymeric membranes have been proven effective in MPs removal. However, fouling is the main drawback of membrane processes and MPs can foul the membranes due to their small size and specific surface properties. Hence, it is important to investigate the impacts of MPs on membrane fouling to develop efficient membrane-based techniques for MPs removal. Although membrane technologies have a high potential for MPs removal, the interaction of MPs with membranes and their fouling effects have not been critically reviewed. The purpose of this paper is to provide a state-of-the-art review of MPs interaction with membranes and facilitate a better understanding of the relevant limitations and prospects of the membrane technologies. The first section of this paper is dedicated to a review of recent studies on MPs occurrence in WWTPs aiming to determine the most frequent MPs. This is followed by a summary of recent studies on MPs removal using membranes and discussions on the impact of MPs on membrane fouling and other probable issues (abrasion, concentration polarisation, biofouling, etc.). Finally, some recommendations for further research in this area are highlighted. This study serves as a valuable reference for future research on the development of anti-fouling membranes considering these new emerging contaminates.

The motional dynamics of nuclear magnetic resonance (NMR) logging tools can significantly influence the measurement performance of such tools. NMR logging is used for geophysical evaluation in geological environments, primarily quantifying formation porosity and fluid volumes, as well as providing a qualitative estimation of permeability. NMR logging tools are conveyed via two main mechanisms; wireline logging and logging while drilling (LWD). We conduct detailed simulations to quantify the impact of tool motion on NMR measurements during logging. This involves conducting electromagnetic simulations which quantify the magnetic fields generated by a logging tool, and subsequently introducing motion profiles within the relevant spin dynamic calculations. This enables tool motional dynamics to be imposed on the signal acquisition. Several movement profiles are considered: linear axial movement to replicate wireline logging tool motion, as well as axial harmonic and lateral harmonic movement to simulate the shocks and vibrations experienced during logging while drilling. Lateral motion is observed to cause a greater degree of signal attenuation relative to axial motion due to the cylindrical shape of the excited volume. The magnitude of motion (e.g. the velocity of linear motion or the amplitude of harmonic motion) is demonstrated to increase the severity of signal attenuation, as expected. However, the frequency of harmonic motion demonstrates a more complex effect on the measured signal. The harmonic interaction between the motion frequency and measurement frequency (determined by the echo spacing) can cause wave interference which results in enhanced or diminished signal attenuation. Finally, we demonstrate that reducing both the magnetic field gradient as well as the echo spacing reduce the degree of signal attenuation observed during measurement. The results presented in this work demonstrate how the optimisation of key design parameters can be used to control the sensitivity of NMR logging tools towards motion.

Water-oil emulsion formation is commonly observed at wellhead chokes and topsides control valves, with the impact mitigated by chemical injection. The presence of emulsions downhole in Pyrenees wells was inferred from their significant production rate impact and confirmed by the uplift observed from downhole chemical injection. The Pyrenees fields are located in the Exmouth sub-basin offshore Western Australia. Through analogy between individual Inflow Control Device (ICD) orifice elements and wellhead chokes, ICDs were suspected as the source. This paper describes experimental confirmation of emulsion formation by orifice type inflow control devices in Pyrenees field horizontal well completions and proceeds to characterise the emulsions formed. A purpose built flow rig combined Pyrenees crude oil and produced water under low shear, simulating reservoir flow conditions, before flowing through an orifice element at rates equal to peak and mid-life production. With liquid flow rate held constant, water cut was increased in 10% steps from 0 to 100% water content. A key component of the experimental system is a benchtop Nuclear Magnetic Resonance spectrometer equipped for non-invasive Pulsed Field Gradient measurement of the Droplet Size Distribution of the emulsions formed. Droplet size distribution is a fundamental fluid property that significantly impacts emulsion rheology. The heavy end component of the crude oil was characterised by a novel Enhanced Saturate Aromatic Resin and Asphaltene analysis procedure to facilitate benchmarking of Pyrenees with emulsion formation tendencies of other producing assets. This quantitative demonstration of emulsion formation by orifice type ICDs at near reservoir conditions is novel, as is observation of partial emulsification, and represents initial steps towards generalisation of models for emulsion formation and their transport properties.

Complex organic molecules are of great importance to research and industrial chemistry and typically synthesized from smaller building blocks by multistep reactions. The ability to perform multiple (distinct) transformations in a single reactor would greatly reduce the number of manipulations required for chemical manufacturing, and hence the development of multifunctional catalysts for such one-pot reactions is highly desirable. Here we report the synthesis of a hierarchically porous framework, in which the macropores are selectively functionalized with a sulfated zirconia solid acid coating, while the mesopores are selectively functionalized with MgO solid base nanoparticles. Active site compartmentalization and substrate channelling protects base-catalysed triacylglyceride transesterification from poisoning by free fatty acid impurities (even at 50 mol%), and promotes the efficient two-step cascade deacetalization-Knoevenagel condensation of dimethyl acetals to cyanoates.

Understanding the uptake and storage of gases by microporous materials is important for our future energy security. As such, we demonstrate here the application of two-dimensional NMR relaxation experiments for probing the admission and corresponding exchange dynamics of methane within microporous zeolites. Specifically, we report low-field (12.7 MHz) 1H NMR relaxation-exchange correlation measurements of methane within commercial LTA zeolites (3A and 4A) at 25 and 35 bar and ambient temperature. Our results demonstrate the clear identification of bulk–pore and pore–pore exchange processes within zeolite 4A, facilitating the calculation and comparison of effective exchange rate dynamics across varying diffusion length scales and gas pressures. Additional data acquired for zeolite 3A reveals the sensitivity of NMR relaxation phenomena to size-exclusive gas admission phenomena, illustrating the potential of benchtop NMR protocols for material screening applications.