Recent Advances in MRI Studies of Chemical Reactors: Ultrafast Imaging of Multiphase Flows

NMR has long been established as an in situ technique for studying the solid-state structure of catalysts and the chemical processes occurring during catalytic reactions. Increasingly, pulsed field gradient (PFG) NMR and magnetic resonance imaging (MRI) are being exploited in chemical reaction engineering to measure molecular diffusion, dispersion and flow hydrodynamics within reactors. By bringing together NMR spectroscopy, PFG NMR and MRI, we are now able to probe catalysts and catalytic processes from the angstrom-to-centimeter scale. This article briefly reviews current activities in the field of MRI studies applied to catalysts and catalytic reactors. State-of-the-art measurements, which can already be used in real reactor design studies, are illustrated with examples of single-phase flow with and without chemical reaction in a fixed-bed reactor. The ability to obtain high spatial resolution (< 200μm) in images of the internal structure and flow field within reactors is demonstrated, and the potential uses of these data in reactor design and understanding bed fouling phenomena are discussed. In particular, MRI has produced the first detailed measurements of the extent of heterogeneity in the flow field within fixed-bed reactors. The example of a fixed-bed esterification process is used to show how NMR spectroscopy and MRI techniques can be combined to provide spatially resolved information on both hydrodynamics and chemical conversion within a process unit. The emerging area of ultrafast MRI is then highlighted as an area of particular interest. Recent advances have demonstrated that it is possible to record 2D images over timescales of ～100ms in the magnetically heterogeneous environments typical of heterogeneous chemical reactors. These advances open up opportunities to image many unsteady state processes for the first time. Examples are given of real-time visualization of bubble-train flow in a ceramic monolith and exploring the stability of the gas–liquid distribution as a function of liquid flow rate in a trickle-bed reactor.     

Nuclear magnetic resonance imaging of an operating gas–liquid–solid catalytic fixed bed reactor

This work reports our pioneering application of the nuclear magnetic resonance imaging (MRI) technique to the dynamic in situ studies of gas–liquid–solid reactions carried out in a catalytic trickle bed reactor at elevated temperature. The major advance of these studies is that MRI experiments are performed under reactive conditions. We have applied MRI to map the distribution of liquid phase inside a catalyst pellet as well as in a catalyst bed in an operating trickle-bed reactor. In particular, our studies have revealed the existence of the oscillating regimes of the heterogeneous catalytic hydrogenation reaction caused by the oscillations of the catalyst temperature and directly demonstrated the existence of the coupling of mass and heat transport and phase transitions with chemical reaction. The existence of the partially wetted pellets in a catalyst bed which are potentially responsible for the appearance of hot spots in the reactor has been also visualized. The combination of NMR spectroscopy with MRI has been used to visualize the spatial distribution of the reactant-to-product conversion within an operating reactor.     

Albumin-Coated Single-Core Iron Oxide Nanoparticles for Enhanced Molecular Magnetic Imaging (MRI/MPI)

Colloidal stability of magnetic iron oxide nanoparticles (MNP) in physiological environments is crucial for their (bio)medical application. MNP are potential contrast agents for different imaging modalities such as magnetic resonance imaging (MRI) and magnetic particle imaging (MPI). Applied as a hybrid method (MRI/MPI), these are valuable tools for molecular imaging. Continuously synthesized and in-situ stabilized single-core MNP were further modified by albumin coating. Synthesizing and coating of MNP were carried out in aqueous media without using any organic solvent in a simple procedure. The additional steric stabilization with the biocompatible protein, namely bovine serum albumin (BSA), led to potential contrast agents suitable for multimodal (MRI/MPI) imaging. The colloidal stability of BSA-coated MNP was investigated in different sodium chloride concentrations (50 to 150 mM) in short- and long-term incubation (from two hours to one week) using physiochemical characterization techniques such as transmission electron microscopy (TEM) for core size and differential centrifugal sedimentation (DCS) for hydrodynamic size. Magnetic characterization such as magnetic particle spectroscopy (MPS) and nuclear magnetic resonance (NMR) measurements confirmed the successful surface modification as well as exceptional colloidal stability of the relatively large single-core MNP. For comparison, two commercially available MNP systems were investigated, MNP-clusters, the former liver contrast agent (Resovist), and single-core MNP (SHP-30) manufactured by thermal decomposition. The tailored core size, colloidal stability in a physiological environment, and magnetic performance of our MNP indicate their ability to be used as molecular magnetic contrast agents for MPI and MRI.     

Two-dimensional nuclear magnetic resonance of resins

A group of resins was synthesised from a series of phenols and aldehydes, and their structures comprehensively deduced from two-dimensional nuclear magnetic resonance spectroscopy (2-D NMR). Correlation spectroscopy, in particular carbon-proton heteronuclear chemical shift correlation spectroscopy, was shown to be especially incisive in assigning structural features to the NMR signals. The method has permitted fuller structural characterisation of these materials than was heretofore possible, and has identified, inter alia, methylene and methyleneoxy bridges unequivocally: complex substitution patterns in the phenol-derived aromatic rings have also been elucidated. It is demonstrably possible to apply the same techniques to similar complex resin structures, and to utilise these structural insights to determine the mechanistic processes involved in their syntheses.     

固体核磁共振技术及其在氟聚合物研究中的应用

固体核磁共振作为一种重要的现代分析研究手段，在许多研究领域都有广泛的用途。通过对常用的固体核磁共振技术的介绍结合其在聚四氟乙烯、聚偏氟乙烯、四氟乙烯-六氟丙烯共聚物分析研究中的应用，说明固体核磁共振技术是研究常见氟聚合物结构和分子运动的重要方法。     

Solution and solid state nuclear magnetic resonance investigation of poly(methylmethacrylate)/ poly(ethylene oxide) blends

It is well known that nuclear magnetic resonance spectroscopy (NMR) is a powerful method to characterize blends compatibility at the molecular level. In this work binary blends formed by poly(methylmethacrylate)/poly(ethylene oxide), PMMA/PEO, were investigated by different solution and solid state NMR techniques to obtain information on blends homogeneity and compatibility. It was characterized that the values of T₁^Hρ obtained by variable contact time and delayed contact time experiments, for each composition, were distinct and this fact suggests that regions with different molecular mobilities exist, as a consequence of blending interaction. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2955–2958, 2003     

PGSE NMR studies of water states of hydrogel P(Am–NaA)

The behavior of absorbed water in equilibrium‐swollen poly(acrylamide‐co‐sodium acrylate) [P(Am–NaA)] hydrogel was studied using the pulsed‐gradient spin‐echo (PGSE) nuclear magnetic resonance (NMR) technique. The observed nonexponential decay of the PGSE signal can be described satisfactorily by a sum of three discrete exponential terms. The self‐diffusion coefficient and amount each of three phases' water can be determined quantitatively. By analysis these data, the swelling ratio of hydrogel P(Am–NaA) system in an equilibrium swollen state can be determined. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 424–427, 2000     

High-throughput determination of oil content in corn kernels using nuclear magnetic resonance imaging

A new high-throughput method for measuring oil content in intact, single corn kernels is demonstrated using nuclear magnetic resonance imaging (MRI) methods. This nondestructive technique enables the evaluation of relative oil content in up to 2,592 corn kernels in less than 40 min using a 1.5 T clinical MRI scanner. Custom software was developed to process and analyze 3-D magnetic resonance (MR) image data rapidly. The precision and accuracy of the MR method for measuring oil content are discussed. The precision of the MRI results is shown to be dependent on MR scanner noise. The MRI results show very good relative accuracy compared with low-field NMR, NIR transmission, and accelerated solvent extraction measurements. Minor differences between the MRI and low-field NMR experimental protocols were shown to be inconsequential to the oil content measurement. Extending the MRI method to the analysis of other oilseeds and/or the use of other magnetic field strengths is discussed, as is a comparison of this MRI method relative to other high-throughput magnetic resonance screening techniques.     

核磁共振法在研究木素和碳水化合物结构方面的应用

本文评述了核磁共振法（ＮＭＲ）在木素和碳水化合物结构方面的 应用情况，介绍了以及它们的应用原理和方法．     

Study of alinite cement hydration by impedance spectroscopy

Two types of alinite cements, Mg-alinite and Zn-alinite, were synthesized using the reagent grade chemicals. Their hydration behavior was compared with ordinary Portland cement (OPC) using impedance spectroscopy (IS) and ²⁹Si nuclear magnetic resonance (NMR) spectroscopy. The bulk resistance in the IS spectra and the intensity ratio of the hydrous (Q₁ and Q₂) to anhydrous (Q₀) phases in the NMR spectra were estimated as the extent of hydration. The results obtained from both techniques were consistent each other. Mg-alinite had a comparable hydration rate to OPC and Zn-alinite exhibited faster hydration kinetics than Mg-alinite.     

NMR imaging of low pressure,gas‐phase transport in packed beds using hyperpolarized xenon‐129

Gas‐phase magnetic resonance imaging (MRI) has been used to investigate heterogeneity in mass transport in a packed bed of commercial, alumina, catalyst supports. Hyperpolarized ¹²⁹Xe MRI enables study of transient diffusion for microscopic porous systems using xenon chemical shift to selectively image gas within the pores, and, thence, permits study of low‐density, gas‐phase mass‐transport, such that diffusion can be studied in the Knudsen regime, and not just the molecular regime, which is the limitation with other current techniques. Knudsen‐regime diffusion is common in many industrial, catalytic processes. Significantly, larger spatial variability in mass transport rates across the packed bed was found compared to techniques using only molecular diffusion. It has thus been found that that these heterogeneities arise over length‐scales much larger than ～100 µm. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4013–4019, 2015     

Recent Advances in Metal-Based Magnetic Composites as High-Efficiency Candidates for Ultrasound-Assisted Effects in Cancer Therapy

Metal-based magnetic materials have been used in different fields due to their particular physical or chemical properties. The original magnetic properties can be influenced by the composition of constituent metals. As utilized in different application fields, such as imaging monitoring, thermal treatment, and combined integration in cancer therapies, fabricated metal-based magnetic materials can be doped with target metal elements in research. Furthermore, there is one possible new trend in human activities and basic cancer treatment. As has appeared in characterizations such as magnetic resonance, catalytic performance, thermal efficiency, etc., structural information about the real morphology, size distribution, and composition play important roles in its further applications. In cancer studies, metal-based magnetic materials are considered one appropriate material because of their ability to penetrate biological tissues, interact with cellular components, and induce noxious effects. The disruptions of cytoskeletons, membranes, and the generation of reactive oxygen species (ROS) further influence the efficiency of metal-based magnetic materials in related applications. While combining with cancer cells, these magnetic materials are not only applied in imaging monitoring focus areas but also could give the exact area information in the cure process while integrating ultrasound treatment. Here, we provide an overview of metal-based magnetic materials of various types and then their real applications in the magnetic resonance imaging (MRI) field and cancer cell treatments. We will demonstrate advancements in using ultrasound fields co-worked with MRI or ROS approaches. Besides iron oxides, there is a super-family of heterogeneous magnetic materials used as magnetic agents, imaging materials, catalytic candidates in cell signaling and tissue imaging, and the expression of cancer cells and their high sensitivity to chemical, thermal, and mechanical stimuli. On the other hand, the interactions between magnetic candidates and cancer tissues may be used in drug delivery systems. The materials’ surface structure characteristics are introduced as drug loading substrates as much as possible. We emphasize that further research is required to fully characterize the mechanisms of underlying ultrasounds induced together, and their appropriate relevance for materials toxicology and biomedical applications.     

Use of magnetic nanoparticles as nanosensors to probe for molecular interactions

Biocompatible magnetic nanosensors have been designed to detect molecular interactions in biological media. Upon target binding, these nanosensors cause changes in the spin-spin relaxation times of neighboring water molecules, which can be detected by magnetic resonance (NMR/MRI) techniques. These magnetic nanosensors have been designed to detect specific mRNA, proteins, enzymatic activity, and pathogens (e.g., virus) with sensitivity in the low femtomole range (0.5-30 fmol).     

Characterization of the micellar structure of a barium nonylphenolate/Barium carbonate complex by nuclear magnetic resonance spectroscopy

The micellar structure of a barium nonylphenolate/barium carbonate complex was characterized by ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy. Several NMR techniques, including measurement of spin-lattice relaxation time, chemical shift variation, and line width of the ¹H NMR signal and solid-state ¹³C NMR data, were used in this study. NMR results indicate that the prepared barium nonylphenolate and barium carbonate complex formed a micelle structure with the oxygen atom of the nonylphenolate ring oriented toward the solid-state center core of barium carbonate while the highly branched aliphatic chain pointed outward to the hydrocarbon solvent.     

Local Velocity and Concentration of the Single Components in Water/Oil Mixtures Monitored by Means of MRI Flow Experiments in Steady Tube Flow

In this paper the spatially resolved determination of velocities in two‐phase systems consisting of water and oil by means of nuclear magnetic resonance (NMR) imaging (MRI) techniques is described and applied to steady tube flows with regard to the total flow rate. As MRI offers the possibility to study the flow of multiphase materials spatially resolved with various forms of contrast, even optically opaque water/oil mixtures can be studied in the interior of the material. Besides snapshot images of the actual flow pattern also local velocity and concentration fields of both phases can be obtained separately. The insight into the inner micro flow processes and microstructure allows to characterize fluid mixtures or emulsions. Flow rate and preparation/mixing method were varied in order to realize changes of the flow pattern and the structure of the mixture during flow. Physical models of the flow behavior and physical stability of these complex systems can be based upon this information.     

Applications of Low Field NMR Techniques in the Characterization of Oil Sand Mining,Extraction and Upgrading Processes

A number of techniques have previously been developed that use low field nuclear magnetic resonance (NMR) relaxometry for conventional and heavy oil reservoir characterization. In the current work, the adaptation of these algorithms for use in the oil sands industry is presented. NMR based methods have been developed for identification of water and bitumen content in ore and froth samples. Consistent algorithms have been used to analyze over 500 ore samples and 50 froth samples from the Athabasca oil sands in northern Alberta. Preliminary analyses are shown, with applications for in‐situ fluid determination using NMR logging tools and improved process control in oil sands processing plants.     

酶在接近无水有机介质中的生物催化特性

介绍了接近无水条件下以悬浮状态存在的酶以及固定化酶生物催化特性。采用电子顺磁共振(EPR)及核磁共振(NMR)研究了水与酶之间的关系。在有机溶剂中加水和不加水情况下,处于悬浮状态的酶及固定化酶结构和功能存在差别。研究发现,尽管以悬浮状态存在的酶和固定化酶结构明显不同,但水含量、酶活性、酶柔性以及活性位点极性之间存在着密切的关系。结果表明,在含水量很少的条件下,水对酶活性位点的生物催化起着关键作用。     

核磁共振技术及其应用进展

核磁共振技术是有机物结构测定的有力手段,不破坏样品,是一种无损检测技术.从连续波核磁共振波谱发展为脉冲傅立叶变换波谱,从传统一维谱到多维谱,技术不断发展,应用领域也越广泛.核磁共振技术在有机分子结构测定中扮演了非常重要的角色,核磁共振谱与紫外光谱、红外光谱和质谱一起被有机化学家们称为"四大名谱".     

NMR Studies of Diffusion-Coherence Phenomena in Red Cell Suspensions: Current Status

Pulsed field-gradient spin-echo (PGSE) nuclear magnetic resonance (NMR) diffusion experiments conducted on some heterogeneous systems have been observed to show periodicities in the data. These “coherence patterns” are manifest in the normalized PGSE signal intensities as a function of the spatial wave vector q in so-called q-space plots. The sample that to our knowledge best reveals these coherence patterns is suspensions of red blood cells (RBC). The origin of these patterns and their mathematical and physical underpinnings are now well established. We have used computer simulations of molecular diffusion in lattices of RBC and other cells to aid in the interpretation and analysis of the corresponding experimental data. The aim of this review is to present the current status of NMR q-space studies of RBC suspensions that show the diffusion-coherence effect.     

NMR, multi-spectroscopic and molecular modeling approach to investigate the complexes between C.I. Acid Orange 7 and human serum albumin in vitro

In this study, the interaction between C.I. Acid Orange 7 (AO7) and human serum albumin (HSA) was firstly investigated using nuclear magnetic resonance (NMR) spectroscopy in combination with fluorescence quenching spectroscopy, three-dimensional fluorescence spectroscopy, UV-vis absorption spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, circular dichroism (CD) spectroscopy and molecular modeling method in vitro. The results of NMR data confirmed that AO7 indeed interacted with HSA, and the hydrophobic portion of AO7 should be embedded to the hydrophobic pocket of HSA. The fluorescence quenching analysis revealed that AO7 can bind to HSA. The conformational change of HSA in the presence of AO7 was confirmed by synchronous fluorescence, three-dimensional fluorescence, UV-vis absorption, FT-IR and CD spectra. The binding distance between AO7 and tryptophan residue of HSA was calculated by the efficiency of fluorescence resonance energy transfer. Molecular modeling showed that hydrophobic force and hydrogen bonds were the major interaction between AO7 and HSA.