Continuous Flow Tube Research Articles

An experimental investigation of PG/VG pyrolysis combined with molecular dynamics

Propylene glycol (PG) and vegetable glycerin (VG) are common ingredients used in the preparation of various products, and notably in e-cigarette liquids. In this work, we investigated the generation of light gases from the pyrolysis of PG, VG and their mixtures. ReaxFF-MD was used to study the elementary reactions involved in the pyrolysis of PG/VG mixtures of 50/50 and 30/70 percent by volume. Main reactions included dehydration, dehydrogenation and C-C bond cleavage. In addition, we focused on the elementary reactions that form the light gases: C2 hydrocarbons, CO, CO2, and H2. Kinetic rates of PG and VG decomposition, and the Arrhenius parameters, were calculated, with errors as low as 1% with respect to pure PG and VG kinetic rate constants. Furthermore, experimental results were obtained by conducting pyrolysis experiments on PG, VG and their mixtures, in a continuous flow tube reactor at reaction temperatures ranging between 550°C and 850°C. The main gas products were predominantly CO, CH4, C2H4, in addition to C2H6, C2H2, H2, and CO2. Gas product concentrations increased with temperature except for ethane, which underwent further decomposition, as expected from the elementary reactions. Liquid mixtures proved to produce more products due to reactions taking place between the different pyrolysis products obtained from PG and VG, as shown by ReaxFF-MD simulations.

Functional asymmetry of the urea transporter UT-B in human red blood cells.

We studied urea, thiourea, and methylurea transport and interaction in human red blood cells (RBCs) under conditions of self-exchange (SE), net efflux (NE), and net influx (NI) at pH 7.2. We combined four methods, a four-centrifuge technique, the Millipore-Swinnex filtering technique, the continuous flow tube method, and a continuous pump method to measure the transport of the 14C-labeled compounds. Under SE conditions, both urea and thiourea show perfect Michaelis-Menten kinetics with half-saturation constants, K½,SE (mM), of ≈300 (urea) and ≈20 (thiourea). The solutes show no concentration-dependent saturation under NE conditions. Under NI conditions, transport displays saturation or self-inhibition kinetics with a K½,NI (mM) of ≈210 (urea) and ≈20 (thiourea). Urea, thiourea, and methylurea are competitive inhibitors of the transport of analog solutes. This study supports the hypothesis that the three compounds share the same urea transport system (UT-B). UT-B functions asymmetrically as it saturates from the outside only under SE and NI conditions, whereas it functions as a high-capacity channel-like transporter under NE conditions. When the red blood cell enters the urea-rich kidney tissue, self-inhibition reduces the urea uptake in the cell. When the cell leaves the kidney, the channel-like function of UT-B implies that intracellular urea rapidly equilibrates with external urea. The net result is that the cell during the passage in the kidney capillaries carries urea to the kidney to be excreted while the urea transfer from the kidney via the bloodstream is minimized.NEW & NOTEWORTHY The kinetics of urea transport in red blood cells was determined by means of a combination of four methods that ensures a high time resolution. In the present study, we disclose that the urea transporter UT-B functions highly asymmetric being channel-like with no saturation under conditions of net efflux and saturable under conditions of net influx and self-exchange in the concentration range 1-1,000 mM (pH 7.2 and 25-38 °C).

Urea transport in human red blood cells: Donor variation compared to chloride, glucose, and water transport.

We determined the permeability (P, cm/s) of unmodified human red blood cells (HRBC) to urea (Pu), chloride (PCl), glucose (Pglu), and water diffusion (Pd) under conditions of self-exchange (SE) with the continuous flow tube method at pH 7.2, 25°C. Among 24 donors, Pu at 1 mM varied >100%. Two of the donors were also tested in 1983. Their Pu had decreased by 77 and 90%. High age in males and Kidd genotype Jk(a+,b+), but not blood types AB0, appear related to low Pu. For one of the two donors, PCl (150 mM, 38°C, pH 7.2), Pglu (1 mM, 38°C, pH 7.2), and Pd (55.5 M, 25°C, pH 7.2) were determined then and now and showed no significant changes with age. The results from six more donors show donor PCl, Pglu, and Pd in the range of ≈1%. PCl and Pglu are vital for the metabolism of cells and tissues, and we see but little donor variation, and so far, no phenotypes without glucose (GLUT1) and anion (AE1) transporters in HRBC. Phenotypes with no urea transporter (UT-B) or no water transporters (aquaporin, AQP1) are registered and are compatible with life. Our results are in line with the concept that the solutes do not share pathways in common. The great donor variation in Pu must be considered in comparative transport physiological studies.

Characterization of New Particle Formation in Soft X-ray Radiolysis Reactor: AMCs-to-Secondary Inorganic Aerosols

Airborne molecular contaminants (AMCs) in cleanrooms should be monitored and controlled tightly to reduce yield loss since they can be converted into nanoparticles or surface haze contamination on semiconductor chips or masks. Soft X-ray radiolysis was developed to detect AMCs as low as the ppt-level by forming secondary aerosols from AMCs under soft X-ray irradiation. However, new particle formation (NPF) using soft X-ray radiolysis has not been well investigated. In this study, we have developed a continuous flow tube reactor to understand NPF from AMCs using soft X-ray radiolysis. The reactor was designed to continuously maintain parabolic laminar flows within the tube reactor and to extend the exposure time of the gas molecules to soft X-rays by increasing the number of reactor modules. With the increase in the concentration of sulfur dioxide (SO2), the size distribution of particles formed by soft X-ray radiolysis also showed enhanced NPF and subsequent particle growth. However, the conversion rates of SO2 into particles decreased simultaneously. The NPF and subsequent particle growth in the reactor were also positively affected by the exposure time to soft X-rays and the residence time. The exposure time was controlled by the number of soft X-ray emitters, and the residence time in the reactor was adjusted by the number of reactor modules and the inlet flow rate. The mixture of ammonia (NH3) with SO2 stabilized the nucleation of particles formed from SO2 but suppressed the particle growth. In contrast, nitrogen dioxide (NO2) suppressed both nucleation and growth of particles formed from SO2. Among the parameters for controlling soft X-ray radiolysis, the soft X-ray intensity had the highest effect on the inorganic AMCs-to-nanoparticle conversion.

Magnetically agitated continuous-flow tube reactors with aspartate ammonia-lyase immobilized on magnetic nanoparticles

Continuous-flow tube reactors agitating the aspartate ammonia-lyase on magnetic nanoparticles by two external permanent magnets within the reaction stream showed AAL-MNPs being the most efficient in the rotating magnets system.

Intensification of Sonocrystallization of CaSO4 in Continuous Operation Using a Tube Sonicator

Residence time distribution (RTD) studies based on the pulse input method have been performed to analyze the behavior of a continuous-flow tube sonicator with subsequent application for sonocrystal...

Segmented tubular synthesis of monodispersed microsized copper oxalate

Monodispersed microsized copper oxalate particles were prepared in a segmented continuous flow tube reactor, and the effect of the main parameters such as organic additive agent, initial copper ions concentration, residence time, and segmented media on the final products were investigated experimentally. The obtained copper oxalate microsized particles were disc-like in the presence of citrate ligand, which was the shape inducer for the precipitated copper oxalate. Thermodynamic equilibrium diagrams of the Cu(II)-oxalate-H2O, Cu(II)-oxalate-citrate-H2O, and Cu(II)-oxalate-EDTA-H2O solution systems were drawn to estimate the possible copper species under the experimental conditions and to explain the formation mechanisms of copper oxalate particles in the segmented fluidic reactor. Both theoretical and experimental results indicated that the presence of chelating reagents such as citrate and EDTA had distinct effect on the evolution of particle shape. Air and kerosene were tested as media for the fluidic flow segmentation, and the latter was verified to better promote the growth of copper oxalate particles. The present study provides an easy method to prepare monodispersed copper oxalate microsized particles in a continuous scaling-up way, which can be utilized to prepare the precursor material for conductive inks.

Fabrication of calcium phosphate nanoparticles in a continuous flow tube reactor

Fabrication of calcium phosphate nanoparticles in a continuous flow tube reactor

Palladium-N-heterocyclic carbene (NHC) catalyzed C–N bond formation in a continuous flow microreactor. Effect of process parameters and comparison with batch operation

In this work, the Buchwald–Hartwig aryl amination is reported in a home-made continuous plug flow tube microreactor, using a homogeneous well-defined palladium-N-heterocyclic carbene (NHC) complex. The microreactor enabled a 100% conversion of the reagents within 30min, even at very low catalyst concentrations. A direct comparison between batch and continuous flow reactions is described and shows that the Buchwald–Hartwig reaction is faster in the microreactor than in the batch case. An investigation of the influence of the operating parameters of the microreactor on the reaction was carried out. Increasing temperature allowed a faster conversion of the reagents; moreover, no effect on microreactor performance was found by changing tube diameter. The dependence of reaction kinetics on reagents and [Pd(NHC)] pre-catalyst concentrations was investigated based on initial reaction rates. The resulting expression for the rate of reaction showed some similarities with the one reported for palladium–phosphine catalyst, but also some important differences.

Kinetics of O2(1Δ) self-quenching in the O2 — O2(1Δ) — H2O gas mixture

The self-quenching kinetics of O2(1Δ) molecules in the O2 — O2(1Δ) — H2O gas mixture produced by a chemical singlet-oxygen generator for an oxygen—iodine laser is investigated. The rate of change in the O2(1Δ) concentration in continuous-flow tube is determined by measuring the absolute spectral irradiance of the O2 — O2(1Δ) — H2O gas mixture in the ranges of 600 — 800 nm and 1210 — 1330 nm. The effective rate constant of O2(1Δ) deactivation in all possible channels of the O2(1Δ) + O2(1Δ) → products reaction is found to be (8±1.2)×10-17 cm3 s-1.

Development of safe and scalable continuous-flow methods for palladium-catalyzed aerobic oxidation reactions

The synthetic scope and utility of Pd-catalyzed aerobic oxidation reactions has advanced significantly over the past decade, and these reactions have potential to address important green-chemistry challenges in the pharmaceutical industry. This potential has been unrealized, however, because safety concerns and process constraints hinder large-scale applications of this chemistry. These limitations are addressed by the development of a continuous-flow tube reactor, which has been demonstrated on several scales in the aerobic oxidation of alcohols. Use of a dilute oxygen gas source (8% O(2) in N(2)) ensures that the oxygen/organic mixture never enters the explosive regime, and efficient gas-liquid mixing in the reactor minimizes decomposition of the homogeneous catalyst into inactive Pd metal. These results provide the basis for large-scale implementation of palladium-catalyzed (and other) aerobic oxidation reactions for pharmaceutical synthesis.

Neutral super-oxidised solutions are effective in killing P. aeruginosa biofilms

Bacteria growing in biofilms can become up to 1000-fold more resistant to antibiotics and biocides as compared to their planktonic counterparts. As a result of this increased resistance, biofilms and biofilm-related infections cannot be effectively treated with conventional antibiotic therapy. The goal of this study was to determine the efficacy of three neutral pH, super-oxidised solutions (nSOSs, OIS-80, OIS-125, OIS-200, Microcyn Technology) varying in oxychlorine concentration (80, 125 and 200 ppm) against P. aeruginosa grown planktonically and as biofilms. Exposure for 20 s of exponential phase cells to any of the three solutions was sufficient to reduce viability by more than five logs. However, only exposure for 10 min to OIS-125 and OIS-200 for 10 min was sufficient to eradicate stationary phase P. aeruginosa cells. The efficacy of nSOSs on P. aeruginosa biofilms, grown to maturity in continuous flow tube reactors, was determined upon treatment up to 60 min. Viability pre- and post-treatment was determined by CFU counts. The effect of these solutions on P. aeruginosa biofilms and biofilm architecture was further visualised by confocal scanning laser microscopy and quantitatively analysed by COMSTAT. Under these experimental conditions, only OIS-125 and OIS-200 achieved a >3-log reduction and biofilm disaggregation within 30 min of exposure. Because OIS-125 and OIS-200 enhance the disaggregation of biofilms, their use in the treatment of surface-related biofilm infections deserves further investigation.

Continuous flow cracking of waste plastics

Experiments of waste polymers cracking in a continuous flow tube reactor were carried out. The main components of the reactor unit were a screw extruder as a waste plastics feeder and a tube cracking reactor equipped with an internal screw mixer. Cracking process was realized at the temperature range 420–480 °C and raw material feeding rate from 0.3 up to 2.4 kg/h. The principal process products, gaseous and liquid hydrocarbon fractions, are similar to the refinery cracking products. They are unstable due to the high olefins content (especially from polystyrene cracking) and their chemical composition and properties strongly depend on the applied feed composition, i.e. shares of polyethylene, polypropylene and polystyrene. The material balance experiments showed that the main products, liquid or solid materials in ambient temperature, contain typically 20–40% of gasoline fractions (range of boiling point 35–180 °C) and 60–80% of light gas oil fractions (initial boiling point>180 °C). The solid carbon residues are similar to coal cokes and contain even of 50% mineral components. Their calorific values attain 20 MJ/kg and they are solid fuels of quality similar to brown coals.

Hydrogen in education—a biological approach

Hydrogen gas is regarded as a potential candidate for a future energy economy. The change towards new energy systems with hydrogen gas as an energy carrier will have an immense impact on society. Thus, an integrate part of current research and development must be the inclusion of the new technology into public education. By means of a model bioreactor for light-dependent (photobiological) production of hydrogen gas with green algae, we try to serve this goal in biological education. Various simple photo-bioreactor types (closed batch, open batch) were analyzed for their capability to produce hydrogen under different conditions. The focus laid on functionality and simplicity rather than on high efficiency. Easy-to-handle systems that can be used in the classroom are presented. In a more sophisticated version a proton exchange membrane (PEM-) fuel cell was connected to a continuous gas flow tube bioreactor. We developed a software interface, designed to read light intensity, temperature and power generation by the bioreactor and the connected fuel cell, respectively. Thus, this bioreactor is specially aimed at integrative teaching in natural science and computer technology at middle and high school level.

An Empirical Approach to Correlate Power Law Fluid Parameters Obtained from Low Shear Rate Rotational Viscometers and Tube Flow Viscometers

Methods for pressure drop estimation of non-Newtonian power law fluids in tube flow are reviewed. Pressure gradients and the corresponding mass flow rates of five different non-Newtonian fluid foods: 1% solutions of sodium alginate and CMC, 1. 5% CMC solution, two different tomato ketchups, oyster sauce, in four different diameter stainless steel tubes ranging from 7. 51 to 16. 34 mm i. d. were recorded using a continuous flow tube viscometer capable of operating in both transient and continuous flow modes. The fluids were pseudoplastic in nature and followed the power law model. The flow was confined to the laminar flow regime and appreciable slippage occurred in all cases. Power law parameters, based on tube flow and low shear rate rotational viscometer were determined and compared. These power law parameters failed to give the classical relationships proposed by Dodge and Metzner [1]. Empirical equations were developed to correlate power law parameters based on low shear rate rotational viscometer to the ones based on tube flow viscometer. Pressure drop estimations based on the empirical equations followed the experimental values with 139 average absolute error.

The Corrosion of Sol−Gel-Coated Type 316 SS in Chlorinated SC Water

The corrosion mechanism of type 316 SS wire was investigated with and without sol-gel-applied TiO 2 coatings on exposure to HCl under SCWO conditions. The SCWO experiments were carried out in a semi-batch, continuous-flow tube reactor with 5 vol % air and feed streams containing 0.1, 0.2, or 0.5 N HCl. The corrosion was characterized using mass loss, scanning electron microscopy, and energy-dispersive X-ray analysis. Inductively coupled plasma atomic emission spectroscopy was used to analyze the reactor effluent. Sols were prepared from titanium isopropoxide and applied by a dip coating process. The thermal and phase transition behavior of the powders obtained from the sols was characterized using simultaneous TGA/DTA, wide-angle XRD, and micro-Raman spectroscopy. A pitting corrosion mechanism in which the HCl acts as both a catalyst and a reactant was proposed. The results obtained with the TiO 2 -coated wire suggest that the applied coatings were permeable to super- and subcritical water.

A Kinetic Study of the SCWO of a Sulfonated Lignin Waste Stream

The kinetics of the supercritical water oxidation (SCWO) of a sulfonated lignin waste from an industrial source was investigated using a semi-batch, continuous-flow tube reactor. Experiments were carried out at reduced pressures from 0.9 to 1.4 and reduced temperatures from 0.9 to 1.2. In addition, the feed concentration, excess oxidant, flow rate in the reactor, and reactor length were varied to obtain a wide range of experimental residence times and conversions. The residence time and conversion data were used to calculate the reaction orders and Arrhenius parameters. The kinetic model was validated by comparison of the predicted to the experimental conversions. Overall, the results of the kinetic analysis were found to compare very favorably with those from model compound studies in the literature. Based on these results, it was concluded that the overall rate-limiting step was the oxidation of the sufonated lignin ring C−C bonds.

The asymmetry of chloride transport at 38 degrees C in human red blood cell membranes.

Band 3-mediated Cl- exchange in human red blood cells and resealed ghosts was measured at 38 degrees C by the continuous flow tube method. When external Cl- concentration, C(o), is varied with constant internal Cl- concentration, C(i), the flux fits a simple Michaelis-Menten saturation curve (MM fit), with K1/2o = 3.8 +/- 0.4 mM. When the Cl- concentration is varied simultaneously at both sides of the membrane in resealed ghosts (C(i) = C(o) = C(i = o)), the flux rises toward a flat maximum between 200 and 450 mM Cl-, and then decreases at very high C(i = o). An MM fit to the data with C(i = o) < 500 mM gives K1/2s of 106 +/- 13 mM; fits including modifier site inhibition (MS fit) give an over threefold higher K1/2s. Despite this uncertainty, the intrinsic asymmetry of unloaded transport sites, A (defined as E(o)/E(i) with C(i) = C(o), where E(i) is the fraction of unloaded inward-facing sites and E(o) is the fraction of unloaded outward-facing sites), calculated from K1/2s and K1/2o, ranges only from 0.046 to 0.107. A new method, which uses the initial slope of a plot of Cl- flux versus C(i = o), gives A values of 0.023 to 0.038. Flufenamic acid (FA) inhibits Cl- exchange by binding to an external site different from the transport site. At 38 degrees C, FA binds 24-36 times more tightly to E(o) than to E(i). Estimates of A from FA inhibitory potency range from 0.01 to 0.05. All methods, including bicarbonate data from the preceding paper, indicate that at 38 degrees C, like 0 degree C, far more band 3 molecules are in the E(i) than in the E(o) form. The agreement of various methods supports the ping-pong model for anion exchange, and demonstrates that the intrinsic asymmetry is very slightly, if at all, affected by temperature.

Kinetics of bicarbonate transport in human red blood cell membranes at body temperature.

We studied unidirectional [14C]HCO3- efflux from human resealed red cell ghosts with 1 mM acetazolamide under self-exchange conditions at pH = pH(i = o) 7.4-9.0 and 0-38 degrees C by means of the Millipore-Swinnex and continuous flow tube filtering techniques. 14CO2 loss from cells to efflux medium and further to the atmosphere was insignificant. [14C]HCO3- efflux was determined at pH 7.8, 38 degrees C under symmetric variation of the HCO3- concentrations (C(i = o)), and asymmetric conditions: C(i) varied, C(o) constant, or C(o) varied, C(i) constant. MM-fit, Jeff = Jmaxeff x C x (C + K1/2)-1, used to describe the concentration dependence of Jeff,o when only C(o) varied, yields at C(i) = 50 mM: K1/2o = 3.8 mMJ, Jmaxeff.o = 20 nmol cm-2 s-1; at C(i) = 165 mM: K1/2o = 10 mM, Jmaxeff.o = 32 nmol cm-2 s-1. When C(i) varied, noncompetitive self inhibition by HCO3- binding (inhibitor constant K1) to an intracellular site was included (MS-fit). Under conditions of (a) symmetry: C(i = o) = 9-600 mM, K1/2s = 173 mM, K1 = 172 mM, and Jmaxeff,s = 120 nmol cm-2 s-1, (b) asymmetry: C(o) = 50 mM, K1/2i = 116 mM, K1 = 136 mM, and Jmaxeff,i = 92 nmol cm-2 s-1. All flux parameters accord with the ping-pong model for anion exchange. The data for C(i) < 200 mM also fit well to the MM equation, but K1/2 and Jmaxeff are different from the MS-fit and are inconsistent with the ping-pong model. Thus, self-inhibition (MS-fit) must be included even at low concentrations. As at 0 degree C, the system is asymmetric: 8-10 times more unloaded transport sites face inward than outward when C(i = o). Jeff,s was not mono-exponentially dependent on temperature at 0-38 degrees C, indicating that the transmembrane anion transport is controlled by several rate constants with different temperature dependencies. Jeff,s was not significantly affected by increasing pH(i = o) from 7.4 to 7.8, but it decreased by 50% when pH was raised to 9.0.

Catalytic Combustion of Propane and Natural Gas over Silica-Fibre Supported Catalysts

ABSTRACT Different knitted silica-fibre supported metal oxides (oxides of Co, Ni, Mn, Cr) and various combinations of them, platinum-activated cobalt and nickel oxide catalysts as well as noble metal (Pt, Pd) catalysts were prepared. The catalysts were tested for their activity in propane and natural gas combustion in a continuous flow tube reactor at temperature range of 423-823 K and GHSV of 23900 and 47800 h−1. High combustion efficiencies were obtained by the metal oxides and platinum activated metal oxides. Co3O4 was found to be the most active single metal oxide catalyst in propane combustion. The low temperature activity of metal oxide was strongly improved by use of platinum as an activator. The propane combustion over Pd/SiO2 was found to be structure sensitive under our experimental conditions. The dependence of the rate of propane combustion over noble metal containing catalysts was found to be zero order with respect to oxygen and one with respect to propane. The reaction orders over metal oxi...