High Mass Transfer Rates Research Articles

Combination of adsorption-diffusion model with CFD for study of desulfurization in fixed bed

A 2D porous media Computational Fluid Dynamics (CFD) model is developed for a fixed bed adsorber to remove the 4,6-dimethyldibenzothiophene (4,6-DMDBT) from diesel. The Ag-TiO2-SiO2 modified by CeOx adsorbent is used to remove the 4,6-DMDBT from diesel and proves that CeOx species could promote high dispersion of Ag species on adsorbent surface. The mass source term describing mass transfer of 4,6-DMDBT inside the adsorption bed column is considered. The effects of various parameters such as feed concentration, feed rate and column height on adsorption process have been investigated. Mesh independent test is performed to investigate the effect of the grid size on the simulation results. The component distribution contour and mass transfer rate are employed to analyse further the mass transfer phenomenon in fixed bed column. The higher mass transfer rate at the beginning can be observed and the lower mass transfer rate is obtained after a period of adsorption time at high feed concentration. Results also demonstrate that the porous media CFD model can successfully describe the adsorption of 4,6-DMDBT from diesel in fixed bed column. Finally, the results of Genetic algorithm search suggest that the optimal height of mass transfer zone can be got at low feed rate, high bed height and low feed concentration.

Acceleration of lean aqueous hydroformylation in an innovative jet loop reactor concept

The lean biphasic aqueous hydroformylation without chemical additives of the long chain olefin 1-octene using the simple ligand triphenyl trisulfonate sodium salt was investigated in an innovative jet loop reactor on miniplant scale. This elaborate reactor type offers a unique mixing characteristic and is optimised in terms of mechanical energy transfer into the reaction medium through a jet nozzle and organic phase volume fraction. Both variables are important factors in the emulsification of two immiscible liquids. It is subsequently compared to a standard stirred reactor which was also individually optimised. Both concepts showed individual advantages in terms of productivity and catalytic activity. While the jet loop reactor reached high turnover frequencies of 7640h−1 the stirred tank reactor showed high space time yields of up to 12.6·10−5kmolm−3s−1. At very low amounts of dispersed aqueous catalyst phase even very high catalytic activity (TOF=10,960h−1) was observed in the jet loop reactor. High reactivity could also be preserved in a long time run leading to a total turnover number of 76,500. The jet loop reactor enabled high mass transfer rates for the substrate gases of up to 0.28s−1 for H2 and 0.21s−1 for CO resulting in a mass transfer multiple times faster than the obtained reaction rates. To increase regio-selectivity the bidentate ligand sulfoxanthphos was applied which increased the regio-selectivity up to l:b=53 but reduced catalytic activity.

Long‐term activity of QU Car

This paper presents an analysis of the long‐term activity of the cataclysmic variable (CV) QU Car using CCD (charge‐coupled device) V‐band ASAS (All Sky Automated Survey) data, obtained between 2001 and 2009. I show that the evolution of brightness on the timescale of weeks and months (not from night to night) dominates the light curve during this mapped time. The histograms of brightness are not consistent with the normal distribution and show that the character of the light curve changes for the individual years, although the mean brightness remains similar. One episode of an exceptionally bright state displayed a return accompanied by a series of strong fluctuations of brightness. This shows that the amplitude of the brightness variations changes from time to time, and it does not always depend on the mean level of brightness. This analysis of QU Car thus shows the type of the long‐term activity in a CV with a very high mass transfer rate.

Void fraction, bubble size and interfacial area measurements in co-current downflow bubble column reactor with microbubble dispersion

Microbubbles dispersed in bubble column reactors have received great interest in recent years, due to their small size, stability, high gas-liquid interfacial area concentrations and longer residence times. The high gas-liquid interfacial area concentrations lead to high mass transfer rates compared to conventional bubble column reactors. In the present work, experiments have been performed in a downflow bubble column reactor with microbubbles generated and dispersed by a novel mechanism to determine the gas-liquid interfacial area concentrations by measuring the void fraction and bubble size distributions. Gamma-ray densitometry has been employed to determine the axial and radial distributions of void fraction and a high speed camera equipped with a borescope is used to measure the axial and radial variations of bubble sizes. Also, the effects of superficial gas and liquid velocities on the two-phase flow characteristics have been investigated. Further, reconstruction techniques of the radial void fraction profiles from the gamma densitometry's chordal void fraction measurements are discussed and compared for a bubble column reactor with dispersed microbubbles. Empirical correlations are also proposed to predict the Sauter mean bubble diameter. The results demonstrate that the new bubble generation technique offers high interfacial area concentrations (1000–4500 m2/m3) with sub-millimeter bubbles (500–900µm) and high overall void fractions (10–60%) in comparison with previous bubble column reactor designs.

Transient Study of Adsorbed Oxygen Species Arising from Exposure to Dissolved Oxygen

The oxygen reduction reaction (ORR) was studied using Pt based microelectrodes under different mass transfer regimes. Current transients at different potentials were recorded by first applying a cleaning waveform and a rest potential 1–3 transformed to sampled current voltammograms and finally normalised using the equation proposed by Mahon and Oldham 4. In the steady state, the normalised current is akin to an apparent number of electrons n app, while for shorter times, the presence of an extra current that is attributed to the reduction of oxygen adsorbed species (adspecies) can be seen 2,3. These adspecies are only observed after exposure of the surface to dissolved oxygen during the rest potential and their reduction was tested with different types of Pt electrodes. First, Pt nanoparticles were deposited on carbon fibre microdisc electrodes (7 μm Ø). The normalisation gave n app = 3 at steady state conditions; this value is large for an electrode of this size 5 and it is believed that this is due to the effectiveness of the nanoparticles to reduce peroxide towards water due to their close proximity with each other. At shorter times, the normalisation showed an extra current attributed to the reduction of oxygen adspecies 2,3 but also to the reduction of carbon functionalities. To solve this, carbon nanoelectrodes were electroplated with Pt until sub-micron spheres were obtained and covered the carbon surface completely. At the steady state, n app = 2. Since no carbon was exposed to the solution, this n appis attributed to the high rate of mass transfer that can be achieved with these electrodes. At short timescales, the extra current due to the reduction of oxygen adspecies was also visible. Different sizes of Pt microdiscs were also used (5, 10, 25 and 50 μm Ø). The value of n app for each electrode agrees with those reported under steady state conditions 5. Using the equation proposed by Mahon and Oldham 4, a subtraction between the experimental and theoretical current densities was obtained and integrated to calculate the charge density associated to the reduction of the oxygen adspecies. The results from the millisecond to the second scale showed a value of 55 μC cm-2 in agreement with previous works 2,3. This value corresponds to 0.1 monolayers and seems to indicate that the coverage does not depend on the electrode size. Further analysis of the current transients assuming a first order process for the rate of reduction of the oxygen adspecies suggests that the maximum coverage that can be obtained corresponds to approximately 0.3 monolayers. This is currently being studied by recording current transients at the microsecond scale. The dependency of the rate of reduction of the oxygen adspecies on the applied potential is also under study. It is expected that this work will help elucidate the lifetime of the processes involved, namely the reduction of oxygen adsorbed species and the reduction of diffusion controlled oxygen that comes from the bulk. Overall these transient experiments shed new light on the interaction between dissolved oxygen and Pt electrodes and provide new insight on the oxygen reduction reaction. (1) Perry, S. C.; Al Shandoudi, L. M.; Denuault, G. Sampled-Current Voltammetry at Microdisk Electrodes: Kinetic Information from Pseudo Steady State Voltammograms. Anal. Chem. 2014, 86(19), 9917–9923. (2) Perry, S. C.; Denuault, G. Transient Study of the Oxygen Reduction Reaction on Reduced Pt and Pt Alloys Microelectrodes: Evidence for the Reduction of Pre-Adsorbed Oxygen Species Linked to Dissolved Oxygen. Phys. Chem. Chem. Phys. 2015, 17(44), 30005–30012. (3) Perry, S. C.; Denuault, G. The Oxygen Reduction Reaction ( ORR ) on Reduced Metals : Evidence for a Unique Relationship between the Coverage of Adsorbed Oxygen Species and Adsorption Energy. Phys. Chem. Chem. Phys. 2016, 18, 10218–10223. (4) Mahon, P. J.; Oldham, K. B. Diffusion-Controlled Chronoamperometry at a Disk Electrode. Anal. Chem. 2005, 77(18), 6100–6101. (5) Sosna, M.; Denuault, G.; Pascal, R. W.; Prien, R. D.; Mowlem, M. Development of a Reliable Microelectrode Dissolved Oxygen Sensor. Sensors Actuators, B Chem. 2007, 123 (1), 344–351.

ESTUDO DO PROCESSO DE SECAGEM DA LINHAÇA EM LEITO FLUIDIZADO E EM LEITO DE JORRO

O processo de secagem é uma das operações unitárias mais utilizadas em indústrias químicas, alimentícias e agrícolas. A secagem em leito adquiriu grande atenção nos processos industriais devido a algumas vantagens, tais como uma maior área de contato entre o sólido e o fluido de secagem e altas taxas de transferência de calor e massa. Neste trabalho objetivou-se estudar a cinética do processo de secagem da linhaça em dois sistemas: leito fluidizado e leito de jorro, nas temperaturas de 30, 40, 50 e 60 ºC. A realização do processo de secagem foi feita com uma velocidade equivalente a 1,567 m/s, utilizando o leito fluidizado, e para leito de jorro trabalhou-se com 3,318 m/s. O sistema que apresentou melhor eficiência em relação ao gasto de energia foi o leito fluidizado, enquanto que em relação ao tempo foi o leito de jorro com cone de 45º. Dentre as temperaturas estudadas, a secagem à 60 ºC apresentou um menor gasto de energia e tempo, quando o objetivo foi atingir 8 % de teor de umidade.

Preliminary Investigations on a Novel Rotating Media Liquid-air Contacting Device without Liquid Pool

Abstract Contacting device is a system that bring air and water in contact with each other in evaporative cooling systems while it brings liquid desiccant and air in contact with each other in case of liquid desiccant-based air conditioning systems. They should provide high surface area density for heat and mass transfer and also provide high heat and mass transfer rates in smaller volume with lower electrical power consumption. A novel design of contacting device is presented in this work, where plastic porous cylindrical contact media is used and unlike previous designs, the liquid pool in lower part of the device is eliminated. This would help to utilize the contact surfaces more effectively and reduce power consumption of motor used for rotation of the media as compared to earlier designs in literature. The novel contacting device and the experimental set up were developed and preliminary testing was done. The contact media is 230 mm long with diameter equal to 145 mm, providing surface area density equal to 445 m 2 /m 3 . In a preliminary experiment, the device provided evaporative cooling rate up to 288 W and effectiveness of 33.1%. The performance can be further improved by increasing mass flow rate of water for better wetting, increasing surface density by decreasing porosity and increasing path length of air.

Effects of water flow on intra- and intercolonial variability in bleaching of the zoanthid, Palythoa caribaeorum

The zoanthid, Palythoa caribaeorum, is a good indicator of coral bleaching because it is highly susceptible to bleaching under physiological stresses. We show that water flow accounts for variation in thermal bleaching sensitivity of P. caribaeorum within and between colonies. Sample colonies were exposed to two flow regimes (low=3cms−1; high=15cms−1) and two temperature regimes (low=26.5°C; high=33.5°C) in a unidirectional flume for 48h. Six individual colonies of two sizes (small=2.3±0.2cm; large=7.3±0.4cm in diameter) were tested per flow regime. Degrees of bleaching were measured by zooxanthellae count and chlorophyll a concentration. Bleaching of P. caribaeorum was induced by high temperature. High water flow mitigated bleaching, but there was considerable variation in bleaching within and between colonies. Upstream sides of large colonies bleached less than downstream sides in high flow. High water flow also moderated bleaching of small colonies more than large colonies. One possible explanation for these results is that high mass transfer rates mitigate bleaching. This may be more easily accomplished in small colonies, in which the entire colony tends to be exposed to high water flow; thus, small colonies have an advantage during bleaching events.

Intracellular Concentration Gradients That Mirror External Gradients in Microfluidic Flows: A Computational Analysis.

The generation of stable intracellular concentration gradients is a useful method for local control of cell function, selective manipulation of cellular structures and testing hypotheses related to dynamical intracellular processes. Cell culture in a microfluidic device allows the presentation of a stable gradient of small molecules across a single cell. This method has been used to selectively label mitochondria in portions of the cell, trypsinize specific cellular domains, and trigger receptor-mediated endocytosis in specific portions of the cell. Given the small length scales of a typical cell (~30 μm) and short cytoplasmic diffusive time scales of small molecules, it is surprising that cells can be labeled locally with this method. Here we developed models to explore the parametric space over which stable intracellular concentration gradients can be maintained in a microfluidic device. We show that gradients can develop and be maintained indefinitely for high rates of mass transfer across the membrane compared with diffusion, that is, for Sherwood number greater than 1. We show how these gradients can result in gradients in ligand-receptor binding and enzyme substrate binding. This analysis can help interpret and design microfluidic experiments for cytoplasmic partitioning.

CFD analysis of fluidized beds using wastes from post-consumer carton packaging

Fluidized bed reactors can be used for fast pyrolysis of polyethylene-aluminum composite (LDPE/Al) to achieve good gas-solid mixing together with high rates of heat and mass transfer in bed columns. Pyrolysis of waste from post-consumer carton package (i.e., polyethylene-aluminum composite) reduces the manufacturing costs of new packages as it permits to produce them using the recovered aluminum and polyethylene in the process. Therefore, this research aims at modelling and analyzing the gas-solid flow in fluidized beds composed of sand and LDPE/Al mixtures. For all mixtures used, results show that gas-solid flow can be well described by the Eulerian-Eulerian Granular model coupled with the usage of parameterized Syamlal-O’Brien’s model for momentum transfer between phases. For bed mixtures with up to 20% LDPE/Al composite, the bed pressure drop can be predicted by the model with an error of less than 18%. In addition, for bed mixtures operating at air velocities higher than 50% minimum fluidization, significant segregation of LDPE/Al was not observed. This result indicates that bed mixtures can achieve a good gas-solid contact in the bubble fluidization regime and can be used as a fluidized bed reactor for pyrolysis of wastes from post-consumer carton packages.

EDTA-Cu (II) chelating magnetic nanoparticles as a support for laccase immobilization

Developments in nanotechnology have led to the discovery of new materials, namely, magnetic nanoparticles (MNPs), that present easy surface functionalization and high surface-to-volume ratios. These properties allow a high mass transfer rate and easy removal from a reaction matrix. Simple separation under an external magnetic field makes them a promising immobilization support for enzymes. In this work, new MNPs were prepared by functionalization with EDTA-TMS and characterized by TEM, FTIR and BET analytical techniques, among others. These MNPs were applied as support for laccase immobilization to create a promising biocatalyst. Despite the known chelating nature of EDTA-TMS, its use for surface modification of MNPs for laccase immobilization is a rather unexplored strategy and is reported here for the first time. At pH 3.5, the immobilization process showed approximately 97% of enzymatic activity recovery. The Michaelis-Menten kinetic properties of immobilized laccase showed a lower Vmax and a similar KM compared to free laccase. Regarding operational stability, the immobilized enzyme presented approximately 73% of its initial activity after five sequential reactive cycles. The immobilized enzyme was successfully applied to the biocatalysis of Indigo Carmine dye degradation. These MNPs with immobilized laccase showed important advantages compared to other materials for application in industrial biochemical processes, biocatalysis and biosensors.

When does an old nova become a dwarf nova? Kinematics and age of the nova shell of the dwarf nova AT Cancri

The Z Cam-type dwarf nova AT Cnc displays a classical nova (CN) shell, demonstrating that mass transfer in cataclysmic binaries decreases substantially after a CN eruption. The hibernation scenario of cataclysmic binaries predicts such a decrease, on a timescale of a few centuries. In order to measure the time since AT Cnc's last CN eruption, we have measured the radial velocities of a hundred clumps in its ejecta with SITELLE, CFHT's recently commissioned imaging Fourier transform spectrometer. These range from -455 to +490 km/s. Coupled with the known distance to AT Cnc of 460 pc (Shara 2012), the size of AT Cnc's shell, and a simple model of nova ejecta deceleration, we determine that the last CN eruption of this system occurred $330_{-90}^{+135}$ years ago. This is the most rapid transition from a high mass transfer rate, novalike variable to a low mass transfer rate, dwarf nova yet measured, and in accord with the hibernation scenario of cataclysmic binaries. We conclude by noting the similarity in deduced outburst date (within a century of 1686 CE) of AT Cnc with a "guest star" reported in the constellation Cancer by Korean observers in 1645 CE.

RZ Leonis Minoris bridging between ER Ursae Majoris-type dwarf nova and nova-like system

AbstractWe observed RZ LMi, which is renowned for its extremely short (∼19 d) supercycle and is a member of a small, unusual class of cataclysmic variables called ER UMa-type dwarf novae, in 2013 and 2016. In 2016, the supercycles of this object substantially lengthened in comparison to the previous measurements to 35, 32, and 60 d for three consecutive superoutbursts. We consider that the object virtually experienced a transition to the nova-like state (permanent superhumper). This observed behavior reproduced the prediction of the thermal-tidal instability model extremely well. We detected a precursor in the 2016 superoutburst and detected growing (stage A) superhumps with a mean period of 0.0602(1) d in 2016 and in 2013. Combined with the period of superhumps immediately after the superoutburst, the mass ratio is not as small as in WZ Sge-type dwarf novae, having orbital periods similar to RZ LMi. By using least absolute shrinkage and selection operator (Lasso) two-dimensional power spectra, we detected possible negative superhumps with a period of 0.05710(1) d. We estimated an orbital period of 0.05792 d, which suggests a mass ratio of 0.105(5). This relatively large mass ratio is even above that of ordinary SU UMa-type dwarf novae, and it is also possible that the exceptionally high mass-transfer rate in RZ LMi may be a result of a stripped secondary with an evolved core in a system evolving toward an AM CVn-type object.

Dynamics of the sorption of phosphatidylcholine by mesoporous composites based on MCM-41

The possibility of predicting the breakthrough curves of a phospholipid (PL) during its sorption by mesoporous composites based on MCM-41 using models of the dynamics of sorption that consider the kinetics of adsorption (the Thomas model) and mixed diffusion (the asymptotic model) is demonstrated using phosphatidylcholine (PC) as an example. The effect the kinetic parameters have on the tailing of the sorption front with respect to the mixed diffusion limitation of the sorption of nonpolar biologically active substances (BASes) is shown. It is found that the ordered structure of composite materials based on MCM-41 ensures a high rate of mass transfer and thus little tailing of the sorption front, when compared to sorbents with a lower degree of order (silica gel and polymer materials) during the sorption of a phospholipid under dynamic conditions. Based on calculations of the parameter of pattern Λ under the conditions of the dynamic mode of sorption in mixed diffusion kinetics, it is shown that the sorption of phosphatidylcholine from hexane solutions by mesoporous composites based on MCM-41 allows the sorption chromatographic process to proceed in the most advantageous (quasi-equilibrium) mode.

EVOLUTION OF INTERMEDIATE-MASS X-RAY BINARIES DRIVEN BY THE MAGNETIC BRAKING OF AP/BP STARS. I. ULTRACOMPACT X-RAY BINARIES

ABSTRACT It is generally believed that ultracompact X-ray binaries (UCXBs) evolved from binaries consisting of a neutron star accreting from a low-mass white dwarf (WD) or helium star where mass transfer is driven by gravitational radiation. However, the standard WD evolutionary channel cannot produce the relatively long-period (40–60 minutes) UCXBs with a high time-averaged mass-transfer rate. In this work, we explore an alternative evolutionary route toward UCXBs, where the companions evolve from intermediate-mass Ap/Bp stars with an anomalously strong magnetic field (100–10,000 G). Including the magnetic braking caused by the coupling between the magnetic field and an irradiation-driven wind induced by the X-ray flux from the accreting component, we show that intermediate-mass X-ray binaries (IMXBs) can evolve into UCXBs. Using the MESA code, we have calculated evolutionary sequences for a large number of IMXBs. The simulated results indicate that, for a small wind-driving efficiency f = 10−5, the anomalous magnetic braking can drive IMXBs to an ultra-short period of 11 minutes. Comparing our simulated results with the observed parameters of 15 identified UCXBs, the anomalous magnetic braking evolutionary channel can account for the formation of seven and eight sources with f = 10−3, and 10−5, respectively. In particular, a relatively large value of f can fit three of the long-period, persistent sources with a high mass-transfer rate. Though the proportion of Ap/Bp stars in intermediate-mass stars is only 5%, the lifetime of the UCXB phase is ≳2 Gyr, producing a relatively high number of observable systems, making this an alternative evolutionary channel for the formation of UCXBs.

Novel continuous catalytic hydrogenation process for the synthesis of diacetone-d-allose

Diacetone-d-allose is an important building block for the synthesis of pharmaceutical ingredients. The current batch production process involves a chemical oxidation and a reduction step that include hazardous reagents, produce a large amount of waste and require an extensive downstream processing. Current investigations aim to develop a catalytic reduction process of the intermediate diacetone-d-ketoglucose (DAKG) with molecular hydrogen, a green solvent, and a heterogeneous metal catalyst. Improvement of productivity and simultaneous reduction of the environmental impact shall be achieved by transforming the conventional batch procedure into a continuous process with a stationary catalyst packing.The screening studies presented in this work revealed that high reaction rates and a high selectivity (>98%) can be achieved with a commercial platinum catalyst under mild conditions in an aqueous buffer solution. Transition from batch into a continuous process was realized in several mini-scale fixed bed reactors to provide a fast screening and high mass transfer rates. A high selectivity (99%) and a conversion of 30% was achieved. The results indicate that the reactor performance was influenced by internal diffusion limitations and also by external mass transfer. To attain full conversion of DAKG, the reaction was performed in a random packed bed reactor and a selectivity of >96% was achieved.

Simultaneous enrichment of denitrifying anaerobic methane-oxidizing microorganisms and anammox bacteria in a hollow-fiber membrane biofilm reactor.

In this study, the coculture system of denitrifying anaerobic methane oxidation (DAMO) microbes and anaerobic ammonium oxidation (anammox) bacteria was successfully enriched in a hollow-fiber membrane biofilm reactor (HfMBR) using freshwater sediment as the inoculum. The maximal removal rates of nitrate and ammonium were 78mgN/L/day (131mgN/m2/day) and 26mgN/L/day (43mgN/m2/day), respectively. Due to the high rate of methane mass transfer in HfMBR, the activity of DAMO archaea continued to increase during the enrichment period, indicating that HfMBR could be a powerful tool to enrich DAMO microorganisms. Effects of partial methane pressure, temperature, and pH on the cocultures were obvious. However, the microbial activity in HfMBR could be recovered quickly after the shock change of environmental factors. Furthermore, the result also found that DAMO bacteria likely had a stronger competitive advantage than anammox bacteria under the operating conditions in this study. High-throughput sequencing 16S rRNA genes illustrated that the dominant microbes were NC10, Euryarchaeota, Proteobacteria, Planctomycetes, and Chlorobi with relative abundance of 38.8, 26.2, 13.78, 6.2, and 3.6%, respectively.

Importance of uniform distribution of impregnated trioctylphosphine oxide in hollow fiber membranes for simultaneous extraction/stripping of phenol

Abstract Trioctylphosphine oxide (TOPO) was impregnated in polypropylene hollow fiber membranes. The impregnation process was optimized and a uniform distribution of TOPO was achieved within the membrane walls, when the membranes were treated with a carrier solution containing 600 mg/L TOPO, and air-dried for 30 min at a low air flow rate ( Re air = 9.2). The resulting extractant impregnated hollow fiber membranes (EIHFM) were characterized by scanning electron microscopy, water entry pressure, gas permeability and mercury porosimetry analysis, all of which showed significant structural and morphological changes in the EIHFMs; pore size, porosity and tortuosity were estimated to be 0.5 μm, 0.09 and 33, respectively. The EIHFMs exhibited high mass transfer rates and removal efficiency during simultaneous extraction and stripping of phenol. At an initial phenol concentration of 200 mg/L, 99% phenol was extracted from the wastewater within 7 h, whereas more than 91% phenol was recovered in the stripping solution, yielding a concentration factor of 1.79. The performance of the EIHFMs did not change significantly during consequent operations under identical conditions, indicating the stability of impregnation. These results suggest that uniformly impregnated TOPO-based EIHFMs can be promising in the recovery of phenols from wastewater.

A new hydrate based process for drying liquids

We present a novel process for drying chlorine by formation of a clathrate hydrate. Liquid chlorine is dried in a rotor-stator spinning disc (RSSD) heat exchanger, which has heat transfer coefficients up to 10kW/m2/K, independent of the flow rate. Benefits of this novel drying process are (1) compactness of the spinning disc heat exchanger, minimizing material investments, (2) blocking of the equipment by the adhesive hydrates is prevented by the rotation, and (3) no chlorine contamination by drying agents, e.g., sulfuric acid or zeolite. Batch and RSSD experiments were performed with dichloromethane as a model compound for liquid chlorine. Lower crystallization temperatures result in shorter induction times of the hydrate formation and thus faster water removal rates. Higher mass transfer rates at higher rotation speeds have the same effect. The results show that the RSSD heat exchanger facilitates an elegant, energy-efficient water removal process that can be applied to removal of trace amounts of water from hydrate forming liquids.

Microchannel reactor for intensifying oxidation of methanol to formaldehyde over Fe-Mo catalyst

Abstract The paper deals with catalytic oxidation of methanol to formaldehyde in a microchannel reactor (MCR) in view of the process intensification. Every channel in the experimental MCR was 1 mm in diameter, 10 mm in height and was filled with an industrial Fe-Mo catalyst ground to a fraction of 0.15–0.25 mm. Methanol concentration in the feed mixture was 6.5 and 12 mol%, oxygen to methanol molar ratio was 1.5, the temperature was in the range 240–360 °C. Safe processing of the reaction in MCR at methanol concentration as high as 12 mol% makes it possible to reach approximately a 10-fold increase in the specific formaldehyde productivity per unit volume of the catalyst even within the explosive range of oxygen-methanol mixtures. Numerical simulation of the process by use of a continuum model revealed its sufficient consistency with the experimental results. It was shown that methanol conversion decreased by ∼12% after operation for 100 h at 300 °C and 12 mol% of methanol. In contrast, at the same conditions but at standard 6.5 mol% of methanol, the decrease in the conversion did not exceed 3%. The use of MCR for highly exothermic reactions has high potential due to extremely high rates of heat and mass transfer, provided that the catalyst used has stable activity of fine particles during on-stream operation.