Experimental Run Time Research Articles

Convective heat transfer correlation for a single surrogate firebrand and a simplified firebrand pile on a flat plate using naphthalene sublimation in heated air flow

Previous studies have shown that most structure ignitions in wildland urban-interface fires are due to firebrand deposition and ignition. The heat transfer mechanisms involved in firebrand deposition need further study and characterization for better understanding of the firebrand ignition process. In particular, convective heat transfer correlations over a single firebrand and a pile of firebrands are lacking. Using the heat-mass transfer analogy, naphthalene sublimation experiments were conducted to determine convective heat transfer correlations for a single naphthalene cylinder (a surrogate firebrand) and an idealized three-firebrand pile resting on flat plates from mass loss measurements. These experiments were conducted in a wind tunnel using a heated (50 °C) or room temperature air flow (0.5 m/s to 2.1 m/s). There was good agreement between the Nusselt number correlation obtained using heated air and results with unheated airflows. Experiments using heated airflow reduced the experimental run times and uncertainty in mass loss measurements significantly. In general, the single firebrand had higher Nusselt numbers than the individual firebrands in the pile. In the three-firebrand pile, the firebrand at the top of the pile exhibited the highest heat transfer. The naphthalene sublimation technique can be easily extended to obtain convective heat transfer correlations for various firebrand geometries and configurations.

An Integrated Design Study for an Advanced Tokamak to Close Physics Gaps in Energy Confinement and Power Exhaust

A high-level design study for a new experimental tokamak shows that advances in fusion science and engineering can be leveraged to narrow the gaps in energy confinement and exhaust power handling that remain between present devices and a future fusion pilot plant (FPP). This potential new U.S. facility, an Exhaust and Confinement Integration Tokamak Experiment (EXCITE), will access an operational space close to the projected FPP performance regime via a compact, high-field, high-power-density approach that utilizes advanced tokamak scenarios and high-temperature superconductor magnets. Full-device optimization via system code calculations, physics-based core-edge modeling, plasma control simulations, and finite element structural and thermal analysis has converged on a T, MA, m, , D-D tokamak with strong plasma shaping, long-legged divertors, and 50 MW of auxiliary power. Such a device will match several absolute FPP parameters: plasma pressure, exhaust heat flux, and toroidal magnetic field. It will also narrow or close the gap in key dimensionless parameters: toroidal beta, bootstrap fraction, collisionality, and edge neutral opacity. Integrated neutron shielding preserves personnel access by limiting nuclear activation and maximizes experimental run time by reducing site radiation. In addition to design study results and optimization details, parameter sensitivities and uncertainties are also discussed.

Xrd_simulator: 3D X-ray diffraction simulation software supporting 3D polycrystalline microstructure morphology descriptions.

An open source Python package named xrd_simulator, capable of simulating geometrical interactions between a monochromatic X-ray beam and a polycrystalline microstructure, is described and demonstrated. The software can simulate arbitrary intragranular lattice variations of single crystals embedded within a multiphase 3D aggregate by making use of a tetrahedral mesh representation where each element holds an independent lattice. By approximating the X-ray beam as an arbitrary convex polyhedral region in space and letting the sample be moved continuously through arbitrary rigid motions, data from standard and non-standard measurement sequences can be simulated. This implementation is made possible through analytical solutions to a modified, time-dependent version of the Laue equations. The software, which primarily targets three-dimensional X-ray diffraction microscopy (high-energy X-ray diffraction microscopy) type experiments, enables the numerical exploration of which sample quantities can and cannot be reconstructed for a given acquisition scheme. Similarly, xrd_simulator targets investigations of different measurement sequences in relation to optimizing both experimental run times and sampling.

Expanding the Applicability Range of the Generator Column Technique to Measure the Octanol–Air Partition Ratio of Volatile Compounds

Bioaccumulation modeling has identified a lower limit of ∼5 for the log of the octanol–air partition ratio (log KOA) of chemicals that potentially bioaccumulate in air-breathing organisms. Because existing techniques are not well suited to this volatility range (vapor pressure between 1 and 1000 Pa), we adjusted the generator column method to allow for KOA determination of more volatile compounds. We reduced gas flow rates and experimental run times and examined the potential depletion of octanol within the generator column. By recording KOA values for hexachlorobenzene, 1,2,3,4-tetrachlorobenzene, and 1,2,3-trichlorobenzene that agree with earlier measurements, we first confirmed our ability to obtain reliable data with the generator column technique. The log KOA values between 5 and 45 °C for 1,3-dichlorobenzene, trans-decalin, 2,6-dimethyldecane, 1,2,3,4-tetramethylbenzene, hexylcyclohexane, tri-isopropyl phosphate, and tetradecene have been obtained with the technique. The lowest log10 KOA value measured was 4.69 for trans-decalin at 25 °C. Good agreement with predictions made with poly-parameter linear free energy relationships lends confidence to these data. Reducing gas flow rates and experimental run times are key to obtaining reliable KOA data when applying the generator column technique to volatile compounds. Depletion of the octanol concentration in the generator column did not notably affect the KOA obtained from the measurements.

The impact of detection rate changes and correlations on random-coincidence background measurements

Coincidence detection of multiple particles emitted during an experiment can yield a new depth of understanding of the underlying process under study. However, the probability of detecting particles that are generated from the same physical event within a given coincidence time window is generally much lower than that of detecting particles that appear in the same coincidence time window, but were not created from the same physical event, and are therefore detected randomly in coincidence with each other. Thus, accurate and precise methods of measuring this random-coincidence background are essential for a wide variety of fields of science. A method to determine this background directly using the data themselves without any additional experimental run time or fake signals introduced in the data was recently established (O’Donnell, 2016). This method yields a statistical uncertainty on the random-coincidence background that is orders of magnitude smaller than that of the true coincidence data, though the potential for systematic errors of backgrounds from this method was never explored. In this work, we discuss common varieties of correlated and uncorrelated changes in the detection rates of each particle detected in an experiment. We demonstrate here that a correlation between particle detection rates from, for example, an incident particle beam that initiates a physical process of interest, creates systematic errors in the random-coincidence background measurement. We also discuss the impact of a variety of other realistic scenarios for rate changes in experiments. Lastly, a method is introduced to correct for errors in the random-coincidence background from any source, yielding an optimization between statistical precision and eliminating potential lingering systematic errors.

A synthetic microplastic fiber-manufacturing method and analysis of airborne microplastic fiber transport behavior in porous media.

Long-term environmental contamination through microplastic (MP) exposure remains poorly understood and may pose economic and geochemical threats. Notably, only a few studies have been conducted on MP contamination of soils. This study investigated the migration of AMP fibers and their influence on water flow rates through porous media. Multiple columns with diameters of 5 cm and water flow rates of 3 ml/min were filled with glass beads or sand. The particle sizes varied between 3 mm for glass beads and 1-2 or 2-4 mm for sand. A method on how to artificially manufacture MP fibers with sizes ranging from 500 to 1000 μm representing AMP fibers occurring in the environment is introduced. The MP fibers were then introduced into water at varying concentrations that were reported in previous studies. The results revealed that regardless of their concentration, the MP fibers suspended in the water did not clog the porous media. In fact, although the fibers penetrated and accumulated in the soil, they did not disrupt the water flow. We recommend that future research focuses on using MP particles with varying densities and at lower concentrations, to prevent flocculation and increase the experiment run time.

Direct Methylation for Determination of Fatty Acids in Coffee Samples by GC-FID.

The direct methylation method developed in this work for coffee samples allowed the determination of fatty acids using smaller sample amounts (100mg), lower solvent volumes (5mL) and shorter experimental run time (~12min). Hence, the experiments are more economical and collaborate with green chemistry, besides favoring the health of the analyst who handles a smaller amount of solvents in a short period. Design Expert software was employed to determine the optimal concentration of the acid and base (0.7 e 1.75molL-1) and evaluate the sonication time (5min for both procedures). The experiments were carried out on different coffee samples in which the fat content ranging from 10.18% to 14.86%. The relative standard deviation values for intraday and interday were 2.78% and 7.8%, respectively, confirming the good precision of the proposed method for fatty acid derivatization.

A Generic AI-Based Technique for Assessing Student Performance in Conducting Online Virtual and Remote Controlled Laboratories

Due to the COVID-19 pandemic and the development of educational technology, e-learning has become essential in the educational process. However, the adoption of e-learning in sectors such as engineering, science, and technology faces a particular challenge as it needs a special Laboratory Learning Management System (LLMS) capable of supporting online lab activities through virtual and controlled remote labs. One of the most challenging tasks in designing such LLMS is how to assess a student’s performance while an experiment is being conducted and how stuttering students can be automatically detected while experimenting and providing the appropriate assistance. For this, a generic technique based on Artificial Intelligence (AI) is proposed in this paper for assessing student performance while conducting online labs and implemented as a performance evaluation module in the LLMS. The performance evaluation module is designed to automatically detect the student performance during the experiment run time and triggers the LLMS virtual assistant service to provide struggling students with the appropriate help when they need it. Also, the proposed performance assessment technique is used during the lab exam sessions to support the automatic grading process conducted by the LLMS Auto-Grading Module. The proposed performance evaluation technique has been developed based on analyzing the student’s mouse dynamics to work generally with any type of simulation or control software used by virtual or remote controlled laboratories; without the need for special interfacing. The study has been applied to a novel dataset built by the course instructors and students simulating a circuit on TinkerCad. Using mouse dynamics fetching, the system extracts features and evaluates them to determine if the student has built the experiment steps in the right way or not. A comparison study has been developed between different Machine Learning (ML) models and a number of performance metrics are calculated. The study confirmed that Artificial Neural Network (ANN) and Support Vector Machine (SVM) are the best models to be used for automatically evaluating student performance while conducting the online labs with a precision reaching up to 91%.

Deep learning early stopping for non-degenerate ghost imaging

Quantum ghost imaging offers many advantages over classical imaging, including the ability to probe an object with one wavelength and record the image with another (non-degenerate ghost imaging), but suffers from slow image reconstruction due to sparsity and probabilistic arrival positions of photons. Here, we propose a two-step deep learning approach to establish an optimal early stopping point based on object recognition, even for sparsely filled images. In step one we enhance the reconstructed image after every measurement by a deep convolutional auto-encoder, followed by step two in which a classifier is used to recognise the image. We test this approach on a non-degenerate ghost imaging setup while varying physical parameters such as the mask type and resolution. We achieved a fivefold decrease in image acquisition time at a recognition confidence of 75%. The significant reduction in experimental running time is an important step towards real-time ghost imaging, as well as object recognition with few photons, e.g., in the detection of light sensitive structures.

Moistube irrigation (MTI) discharge under variable evaporative demand.

We investigated the conceptual capability of Moistube irrigation (MTI) to discharge under zero applied positive pressure and under varied climatic conditions by inducing an artificial evaporative demand (Ed) or negative pressure around Moistube tubing. This study was premised on the null hypothesis that an artificially induced Ed or negative pressure does not impact MTI discharge. Moistube tubing was enclosed in a 1 m long PVC conduit. A 20 l water reservoir placed on an electronic balance provided a continuous supply of water whilst a three-speed hot air blower facilitated the radiative factor and advection process. The procedure was conducted under varied climatic conditions with three air velocity (ua) treatments namely; 1.2 m.s-1, 2.5 m.s-1, and 3.0 m.s-1 and the experiment run times were 159 h, 134 h and 10 h, respectively. The average temperature (Tave) and relative humidity (RH) data for ua = 1.2 m.s-1 were 53°C and 7.31%, whilst for ua = 2.5 m.s-1, Tave was 56°C and RH = 7.19%, and for ua = 3.0 m.s-1, Tave was 63°C and RH = 6.16%. The experimental data was input into the four variable Penman-Monteith method to compute the evaporative demand (Ed). For each Ed, the instantaneous mass flow rate ([Formula: see text]) was recorded using an electronic balance and subsequently converted to volumetric flow rates. For each of the air velocities, the respective Ed values obtained were 0.16, 0.31 and 0.36 mm.d-1. The Bowen ratios (r) were well below 1 (r < 1), which suggested a sufficient supply of moisture to evaporate. For Ed = 0.16 mm.d-1 the vapour pressure deficit (VPD) was 113.08 mbars, whilst for Ed = 0.31 mm.d-1 and for Ed = 0.36 mm.d-1 the VPD were 129.93 mbars and 150.14 mbars, respectively. The recorded discharges (q) at normalised time (t*) = 1 h for Ed = 0.16 mm.d-1 was 7.67*10-3 l.hr-1.m-1 length, whilst for Ed = 0.31 mm.d-1 q = 14.5*10-3 l.hr-1.m-1 length, and for Ed = 0.36 mm.d-1 q = 20.8*10-3 l.hr-1.m-1 length. The imposed negative pressure causes an exponential increase in Moistube™ discharge, thus disproving the null hypothesis. The higher the evaporative demand the higher the discharge. This phenomenon allows MTI to be used for deficit irrigation purposes and allows irrigators to capitalize on realistic soil matric potential irrigation scheduling approach.

Always Lost but Never Forgotten: Gas-Phase Wall Losses Are Important in All Teflon Environmental Chambers.

Yields of secondary organic aerosol (SOA) formation from oxidation of volatile organic compounds are measured in laboratory chambers and then applied in regional and global models. Gas-phase losses to large Teflon-walled environmental chambers have been recently shown to reduce SOA yields. Historically, most chambers have operated in batch mode. Increasingly, however, continuous flow (CF) mode is being used, in which reactants and products are continuously introduced and exhausted from the chamber. Recent literature reports indicate a belief that SOA yields measured in CF chambers are not affected by gas-phase wall losses (GWL). Here, we use an experimentally-constrained box model to show that gas-phase wall losses impact both types of chambers when run under similar conditions. We find CF experiments do mitigate some effects of gas-phase wall losses after long (>2 days) experiment run times, but they have significant losses for typical literature experiment times of 1 day. However, this mitigation phenomenon is an experiment- and mechanism-dependent, and GWL still affects the absolute SOA yield. Finally, we show that at condensation sink values higher than the wall loss rate a lack of change in yield vs seed surface area does not necessarily indicate whether GWL affects the experiment and does not suggest the magnitude.

Long-term assessment of nanoplastic particle and microplastic fiber flux through a pilot wastewater treatment plant using metal-doped plastics

In recent years, several studies have investigated the flux of particulate plastic through municipal waste water treatment plants (WWTP). Challenges related to time consuming analytical methods have limited the number of sampling points and detection limits have hampered quantification of nanoplastic and microplastic fiber fluxes through WWTPs. By synthesizing nanoplastic particles and microplastic fibers labeled with a rare metal (Pd and In, respectively) which can be measured as a proxy for the plastic itself, we have circumvented major analytical pitfalls associated with (micro)plastic measurements. In this study, we spiked the labeled materials to a pilot WWTP mimicking the activated sludge process (nitrification, de-nitrification and secondary clarification). Using a mass flow model for WWTP sludge, we assessed the behavior of particulate plastic in relation to the removal of organic matter. Triplicate samples were collected from the mixed liquor and from the effluent at least twice weekly over the entire experimental run time of 40 d. Our findings show that in discrete grab samples during steady state conditions, at least 98% of particulate plastics were associated with the biosolids. A positive correlation between total suspended solids (TSS) and plastic concentrations was observed in the sludge as well as in the effluent. Because of the strong association between particulate plastic and TSS, TSS removal is likely a good indicator of plastic removal in a full scale WWTP. Therefore, additional process steps in a full-scale WWTP which further reduce the TSS load will likely retain nanoplastic particles and microplastic fibers effectively and consequently increase the removal rates.

Coal and waste direct liquefaction, using glycerol, polyethylene waste and waste tyres pyrolysis oil. Optimisation of liquids yield by response surface methodology

Coal and waste direct liquefaction was carried out to decrease the hydrocarbons production negative bearing to environment. The wastes studied were glycerol, polyethylene waste and waste tyres pyrolysis oil. Glycerol and waste tyres pyrolysis oil were blended with tetralin and used as solvent for coal direct liquefaction (T = 350–450 °C; N2; waste:tetralin at different weight ratios). Glycerol may be considered as a waste from the production of fatty acid methyl esters (FAME). Waste tyres pyrolysis oil showed to be a good hydrogen donor solvent. Solid polyethylene wastes were mixed with coal and used in coal co-liquefaction tests, which showed to be a good option to produce liquid hydrocarbons for fuels or raw materials for chemical industry. Although liquids yield using waste tyres pyrolysis oil or glycerol were high, respectively 62% wt. and 51% wt., the use of polyethylene allowed increasing them to 80% wt. Different experimental conditions were studied, namely: experimental temperature, run time, solvent type and composition and hydrogen initial pressure. The effect of commercial catalysts on co-liquefaction was also studied and the results obtained were compared with those obtained with coal impregnated with Fe or Mo (1% wt./coal). Response surface methodology (RSM) was used to predict the influence of the main experimental conditions studied on product yields. This methodology resulted to be a good one to predict coal liquefaction and co-liquefaction products yields, as predicted values were similar to experimental data. In addition, RSM approach led to the selection of tetralin as solvent and to the use of coal impregnated with 1% of Mo, as liquids yield increased up to 96% wt.

Carbon capture induced changes in Deccan basalt: a mass‐balance approach

AbstractPrevious studies on the Deccan basalt–water–CO2 interaction were focused on numerical simulations and experimental validation that revealed carbonate formation, but restricted to low temperatures and for a shorter period. However, during prolonged interactions, silicates restricted carbonates from forming, and thus necessitated for comparative mass‐balance calculations of parent basalt, neo‐formed mineral and dissolution products to understand apposite parameters that control the reaction extent and optimal geochemical conditions. To examine these interactions, mass‐balance calculations have been attempted. A gradual increase in HCO3− concentration and basalt dissolution is concomitant with the increase in experimental run time; thus, the pH of the solution is affected. X‐ray diffraction and scanning electron microscope–energy dispersive X‐ray spectrometer analyses revealed the presence of carbonates in the post‐experiment residue (run for a shorter period). Owing to gradual carbonate decrease in the residue, Ca2+, Fe2+ and Mg2+ released from basalt gradually increased in the leachate at 100°C. But with the progression of time at 200°C, more secondary silicates were formed and incorporated Mg2+ and Si4+, which led to a decrease in Mg2+ and Si4+ concentrations in the leachate. Mass‐balance calculations revealed that the maximum amount of CO2 is mineralized (22.88 mol%) from the ions derived from the parent basalt at 100°C under 5 bar CO2 and 70 h of experiment running time. But, for longer periods of experiments, the rate of ionic interactions as well as CO2 mineralization is almost ceased. Thus, the rate of dissolution is affected by temperature, but the amount of CO2 mineralization is directly a function of the basalt–water–CO2 interaction time. © 2019 Society of Chemical Industry and John Wiley &amp; Sons, Ltd.

Long-term CO2 capture-induced calcite crystallographic changes in Deccan basalt, India

Previous basalt carbonation studies under hydrothermal-like conditions suggested high amount of calcite formation in a shorter period which is related to the andesine dissolution. However, CO2 capture-induced structural changes in neo-formed minerals have not been studied in detail. To understand these changes, Rietveld refinement and crystallographic characterization were performed for andesine and calcite residue obtained after basalt–water–CO2 interaction experiments. These results indicate large spontaneous strain within calcite which led to contraction along the c-axis and expansion along a-axis. Thus, contraction/expansion along the c-axes is inversely proportional to a-axis of the calcite and andesine, respectively. Interatomic Ca–O and C–O bond lengths show changes with the experimental run time, signifying mutually inverse relationship. Observed crystal structure distortion is due to variation in the O–M–O bond angle. Ionic bond length between Ca and O atoms decreased after 70 h of experiment run that enabled Ca–O ligand to enter in the phyllosilicates. The Ca–O bond length weakening along c-axis caused shrinkage of calcite crystals. Increased bond length together with the weakened covalent bond between C and O atoms led to calcite degeneration after 80 h of experiments; therefore, no calcite persisted in the system. Thus, basalt carbonation is time-dependent process, where, pCO2 plays sub-ordinate role, but, at a constant temperature.

Permuted Pattern Matching Algorithms on Multi-Track Strings

A multi-track string is a tuple of strings of the same length. Given the pattern and text of two multi-track strings, the permuted pattern matching problem is to find the occurrence positions of all permutations of the pattern in the text. In this paper, we propose several algorithms for permuted pattern matching. Our first algorithm, which is based on the Knuth–Morris–Pratt (KMP) algorithm, has a fast theoretical computing time with O ( m k ) as the preprocessing time and O ( n k log σ ) as the matching time, where n, m, k, σ , and occ denote the length of the text, the length of the pattern, the number of strings in the multi-track, the alphabet size, and the number of occurrences of the pattern, respectively. We then improve the KMP-based algorithm by using an automaton, which has a better experimental running time. The next proposed algorithms are based on the Boyer–Moore algorithm and the Horspool algorithm that try to perform pattern matching. These algorithms are the fastest experimental algorithms. Furthermore, we propose an extension of the AC-automaton algorithm that can solve dictionary matching on multi-tracks, which is a task to find multiple multi-track patterns in a multi-track text. Finally, we propose filtering algorithms that can perform permuted pattern matching quickly in practice.

Partitioning of arsenic between hydrothermal fluid and pyrite during experimental siderite replacement

Arsenian pyrite is the major host mineral of gold in Carlin type gold deposit (CTGD) and forms during the interaction of H2S bearing hydrothermal fluids with Fe-bearing carbonates (e.g., siderite, ankerite, Fe-rich dolomite) in the wall rock. Experimental replacement of siderite at hydrothermal conditions (i.e., 200 °C, Psat) was used to study the parameters that control the formation of CTGD pyrite (i.e., pH, time, aH2S) and the partitioning of As between the hydrothermal fluid and newly formed pyrite.Hydrothermal pyrite formed via replacement of siderite in experiments mainly occurs as two types: 1) porous, massive pyrite at alkaline pH conditions or 2) clusters of dense euhedral to anhedral pyrite grains at slightly acidic conditions (pH <6). Longer experimental run times (2 weeks) lead to formation of type 2 pyrite at alkaline conditions and an increase in euhedral grain sizes in all conditions.Concentration of As in newly formed pyrite depends strongly on the As concentration of the hydrothermal fluid used in the experiment. Calculated partition coefficients vary between 300 and 1700 with lowest D values at high As concentrations of the fluid. In the studied system As−1 substitutes for S−2 as indicated by the correlation of high As with low S concentrations. Experimental findings agree well with previous studies in natural CTGD on As substitution and the partitioning of As between ore stage pyrite and hydrothermal fluids trapped as fluid inclusions.The newly constrained partition coefficients for As help to explain the large heterogeneity in natural CTGD pyrite compositions which is caused by changes in the fluid composition due to the strong partitioning of As into the forming pyrite.

Uranium and Multi-element Release from Orthogneiss and Granite (Austria): Experimental Approach Versus Groundwater Composition

In this study, the release of elements and in particular U from five Austrian orthogneiss and granite samples into a CO2-bearing solution was investigated to describe the initial phase (24 h) of leaching focusing on the impact of ferrous (hydro)oxide formation. Experiments were conducted at ambient temperature by flushing CO2:N2 gas through the reactive solution (pHinitial ~ 4.3) at a liquid:solid ratio of 10:1 with and without a reducing agent. The chemical evolution of the leaching solution was dominated by incongruent dissolution of silicates showing a parabolic kinetic behavior due to protective surface formation most likely caused by precipitation of amorphous FeIII/Al hydroxides. However, the relative distribution of Ca, Mg and Sr in the leaching solution excellently traced the individual bulk rock composition. The mobilization of U was highly prevented under oxidizing conditions by sorption onto ferrous (hydro)oxides, which were precipitating through ongoing silicate leaching. Therefore, the leaching behavior of individual U-bearing minerals was less relevant for U release. At reducing conditions, the above elements were accumulated in the solution, although an oversaturation regarding UIVO2 was calculated. This indicates its inhibited formation within the experimental run time. The composition of experimental leaching solutions did not reflect analyzed groundwater compositions from investigated local rock-type aquifers indicating that reaction rate constants of siliceous rocks significantly differ between values found in nature and in the laboratory. Change in active mineral surface areas with ongoing weathering, accumulation of secondary precipitates, leached layer formation and given reaction time are key factors for distinct elemental release.

Sensitivity enhancement by chromatographic peak concentration with ultra-high performance liquid chromatography–nuclear magnetic resonance spectroscopy for minor impurity analysis

High performance liquid chromatography can be coupled with nuclear magnetic resonance (NMR) spectroscopy to give a powerful analytical method known as liquid chromatography-nuclear magnetic resonance (LC-NMR) spectroscopy, which can be used to determine the chemical structures of the components of complex mixtures. However, intrinsic limitations in the sensitivity of NMR spectroscopy have restricted the scope of this procedure, and resolving these limitations remains a critical problem for analysis. In this study, we coupled ultra-high performance liquid chromatography (UHPLC) with NMR to give a simple and versatile analytical method with higher sensitivity than conventional LC-NMR. UHPLC separation enabled the concentration of individual peaks to give a volume similar to that of the NMR flow cell, thereby maximizing the sensitivity to the theoretical upper limit. The UHPLC concentration of compound peaks present at typical impurity levels (5.0–13.1 nmol) in a mixture led to at most three-fold increase in the signal-to-noise ratio compared with LC-NMR. Furthermore, we demonstrated the use of UHPLC-NMR for obtaining structural information of a minor impurity in a reaction mixture in actual laboratory-scale development of a synthetic process. Using UHPLC-NMR, the experimental run times for chromatography and NMR were greatly reduced compared with LC-NMR. UHPLC-NMR successfully overcomes the difficulties associated with analyses of minor components in a complex mixture by LC-NMR, which are problematic even when an ultra-high field magnet and cryogenic probe are used.

Temperature and pressure effects on the product distribution of PTFE pyrolysis by means of qualitative, in-line FTIR analysis

The results of the depolymerisation of PTFE under steady operating conditions in a semi-automated, continuous depolymerisation system are presented. The influence of temperature and pressure on the selectivity of the three main products of depolymerisation (tetrafluoroethylene (TFE), hexafluoropropylene (HFP), and octafluorocyclobutane (OFCB)) was investigated via qualitative in-line FTIR analysis. No carrier gas was used, with the PTFE feed rate and experimental run time kept constant. The temperature and pressure ranges investigated were: 650 °C–750 °C and <10 kPa–40 kPa. The optimum operating conditions to maximise the three main products were determined using response surface methodology following a three-level face centered composite design. A TFE mole fraction of 0.95 and higher was achieved at operating conditions of ±675 °C and <10 kPa. HFP mole fractions of 0.19 and higher were achieved within the operating range of 744 °C–750 °C and 32 kPa up to 40 kPa. At operating conditions of 750 °C and 40 kPa, OFCB fractions of 0.5–0.55 were achieved. The OFCB and HFP mole fractions achieved differed from those previously mentioned in the literature. Analysis of the determined product specific kinetics indicates that the predominant HFP production pathway at low residence times (<3 s) is via the reaction of TFE with difluorocarbenes. At higher residence times the dominant reaction pathway is the dissociation OFCB.