NEW CONCEPT OF ENERGY-EFFICIENT AND RESOURCE-SAVING APPARATUSES FOR MIXING AND CONJUGATED PROCESSES

Abstract. Principles of new generation of apparatuses allowing developing energy-efficient and resource-saving equipment for chemical production are formulated. The total concept based on seven principles. The practical use of all the principles of this concept is illustrated by the examples for apparatuses on liquid-solid, liquid-liquid, liquid-gas systems. The main idea to minimize power consumption was realized by use of essentially transient movement of processed substance in order to shift the system parameters from the steady state, micro scale reactors, vortical flows

Synthesis of thin titania coatings onto the inner surface of quartz tubes and their photoactivity in decomposition of methylene blue and rhodamine B

An evaporation-deposition coating method for coating the inner surface of long (>1 m) quartz tubes of small diameter has been studied by the introduction of two-phase (gas-liquid) flow with the gas core flowing in the middle and a thin liquid film of synthesis sol flowing near the hot tube wall. The operational window for the deposition of continuous titania coatings has been obtained. The temperature range for the deposition of continuous titania coatings is limited to 105–120 °C and the gas flow rate is limited to the range of 0.4–1.0 L min−1. The liquid flow rate in the annular flow regime allows to control the coating thickness between 3 and 10 micron and the coating porosity between 10% and 20%. By increasing the liquid flow rate, the coating porosity can be substantially reduced. The coatings were characterized by X-ray diffraction, N2 chemisorption, thermogravimetric analysis, and scanning electron microscopy. The coatings were tested in the photocatalytic decomposition of methylene blue and rhodamine B under UV-light and their activity was similar to that of a commercial P25 titania catalyst

Process intensification in photocatalytic decomposition of formic acid over a TiO2 catalyst by forced periodic modulation of concentration, temperature, flowrate and light intensity

The effect of forced periodic modulation of several input parameters on the rate of photocatalytic decomposition of formic acid over a TiO2 thin film catalyst has been investigated in a continuously stirred tank reactor. The kinetic model was adopted based on the literature and it includes acid adsorption, desorption steps, the formation of photocatalytic active sites and decomposition of the adsorbed species over the active titania sites. A reactor model was developed that describes mass balances of reactive species. The analysis of the reactor was performed with a computer-aided nonlinear frequency response method. Initially, the effect of amplitude and frequency of four input parameters (flowrate, acid concentration, temperature and light intensity) were studied. All single inputs provided only a minor improvement, which did not exceed 4%. However, a modulation of two input parameters, inlet flowrate and the acid molar fraction, considerably improved the acid conversion from 80 to 96%. This is equivalent to a factor of two increase in residence time at steady-state operation at the same temperature and acid concentration

Non-thermal plasma for process and energy intensification in dry reforming of methane

Plasma-assisted dry reforming of methane (DRM) is considered as a potential way to convert natural gas into fuels and chemicals under near ambient temperature and pressure; particularly for distributed processes based on renewable energy. Both catalytic and photocatalytic technologies have been applied for DRM to investigate the CH4 conversion and the energy efficiency of the process. For conventional catalysis; metaldoped Ni-based catalysts are proposed as a leading vector for further development. However; coke deposition leads to fast deactivation of catalysts which limits the catalyst lifetime. Photocatalysis in combination with non-thermal plasma (NTP), on the other hand; is an enabling technology to convert CH4 to more reactive intermediates. Placing the catalyst directly in the plasma zone or using post-plasma photocatalysis could generate a synergistic effect to increase the formation of the desired products. In this review; the recent progress in the area of NTP-(photo)catalysis applications for DRM has been described; with an in-depth discussion of novel plasma reactor types and operational conditions including employment of ferroelectric materials and nanosecond-pulse discharges. Finally, recent developments in the area of optical diagnostic tools for NTP, such as optical emission spectroscopy (OES), in-situ FTIR, and tunable diode laser absorption spectroscopy (TDLAS), are reviewed

Non-Thermal Plasma for Process and Energy Intensification in Dry Reforming of Methane

Plasma-assisted dry reforming of methane (DRM) is considered as a potential way to convert natural gas into fuels and chemicals under near ambient temperature and pressure; particularly for distributed processes based on renewable energy. Both catalytic and photocatalytic technologies have been applied for DRM to investigate the CH4 conversion and the energy efficiency of the process. For conventional catalysis; metaldoped Ni-based catalysts are proposed as a leading vector for further development. However; coke deposition leads to fast deactivation of catalysts which limits the catalyst lifetime. Photocatalysis in combination with non-thermal plasma (NTP), on the other hand; is an enabling technology to convert CH4 to more reactive intermediates. Placing the catalyst directly in the plasma zone or using post-plasma photocatalysis could generate a synergistic effect to increase the formation of the desired products. In this review; the recent progress in the area of NTP-(photo)catalysis applications for DRM has been described; with an in-depth discussion of novel plasma reactor types and operational conditions including employment of ferroelectric materials and nanosecond-pulse discharges. Finally, recent developments in the area of optical diagnostic tools for NTP, such as optical emission spectroscopy (OES), in-situ FTIR, and tunable diode laser absorption spectroscopy (TDLAS), are reviewed

Intensification of Droplet Disintegration for Liquid–Liquid Systems in a Pulsating Flow Type Apparatus by Adding an Inert Gas

Experimental studies have revealed that the introduction of a small amount (0.5% by volume) of permanent and chemically inert gas bubbles leads to the intensification of droplets disintegration in a liquid–liquid system (emulsification) in a pulsating flow type apparatus. The liquids used were water (continuous phase) and oil (dispersed phase) at room temperature, and nitrogen was used as a gas. The gas hold-up φin was varied in the range of 0% to 4%. The volume fraction of the dispersed phase (oil) was 1% with respect to the continuous phase. The size of the oil droplets was determined by microphotographs; at least 600 drops were photographed in each experiment. The optimal gas hold-up in terms of the highest interfacial area (for the studied conditions) was found to be 0.5%, at which value the droplets’ Sauter mean diameter d32 decreased 1.88 times, and the maximum droplet size decreased 1.3 times, compared with the case without gas input. The effect of decreasing the average droplet size d32 upon the injection of an inert gas in the continuous phase disappears at φin ≈ 2%. The pressure loss at φin ≤ 2% within the measurement error remained constant, while at 4%, it increases by only 5.4%. The role of an inert gas is explained by several factors: (i) a redistribution of momentum over the volume of liquid; (ii) the occurrence of microflows near bubbles and drops, which leads to an increase in shear stresses on the surface of the drops; and (iii) gas bubbles act as pseudocavitation bubbles, whereby when they collapse, they break up adjacent droplets

Influence of Hydrodynamic Conditions on Micromixing in Microreactors with Free Impinging Jets

An experimental study and mathematical modeling of micromixing in a microreactor with free impinging jets (MRFIJ) with a diameter of 1 mm was carried out. In the experimental part, the iodide-iodate technique was used (involving parallel competing Villermaux–Dushman reactions with the formation of I3−). Theoretical assessment revealed that more than 50% of the introduced energy is dissipated in the jets collision region. Through the use of differentiated sampling, an uneven quality distribution of micro mixing in the central and peripheral zones of the reactor was found: at moderate flow rates (700–1000 mL/min, jets velocity of 15–21 m/s) the micromixing in the central part of reactor is up to 12 times better than that in the periphery. Furthermore, the weight fraction of the probes in the central zones of MRFIJ is reduced with increasing jet velocity; this effect is attributed to a more intense formation of ligaments and droplets upon collision of jets and their secondary mixing on the walls of the apparatus. In terms of the weighted average concentration, the best quality of micromixing in the samples is achieved at a flow rate of 300 mL/min. With an increase in the flow rate (and velocity) of the jets, the dependence of the I3− concentration on the flow rate has a nonmonotonic character, which is explained by a change in the nature of the flow in the collision zone of the jets: the transition from the formation of a liquid sheet to the intensive formation of ligaments and drops and secondary mixing of the liquid film formed on the walls of the reactor. The effect of “freshness” of solutions on the concentration of reaction products was studied

Gas–Liquid Two-Phase Flow and Heat Transfer without Phase Change in Microfluidic Heat Exchanger

This work presents an experimental study of the possibility of intensifying in microfluidic heat exchangers (MFHE) by creating a two-phase segmented flow (gas–liquid). Measurements of convective heat transfer were carried out using an MFHE, consisting of six channels 1 × 1 mm. Experimental studies have shown that segmented flow makes it possible to increase the Nusselt number of a laminar flow in MFHE up to 1.67 and reduce thermal resistance up to 1.7 times compared to single-phase flow. At the same time, it was found that the intensification of heat exchange by a two-phase flow is observed only for the range of the volume fraction of gas from 10 to 30%. In addition, the calculation of the thermal performance criterion, including both thermal and hydraulic parameters (friction factor), also confirmed the promise of using the Taylor segmented flow as a method for single-phase heat transfer intensifying in microchannels

Development of a microkinetic model for non-oxidative coupling of methane over a Cu catalyst in a non-thermal plasma reactor

A surface microkinetic plasma model for non-oxidative coupling of methane into H2 and higher hydrocarbons was developed over a Cu catalytic film. Twenty key plasma species including electron, ions, radicals, and neutrals were considered in respective chemical reactions leading to the formation of C2 hydrocarbons onto the catalyst surface. The kinetic model was coupled with a global plasma model to describe the performance of a non-thermal plasma reactor. In the reactor model, the reactant gas flows between the two coaxial cylindrical metal electrodes with a length of 50 mm and a diameter of 2 mm (inner) and 6 mm (outer electrode) coated with a Cu film. The effect of discharge power, initial CH4 concentration, and inlet flow rate on methane conversion was investigated. The surface model shows that the CH4 conversion of 47% is obtained at a discharge power of 70 W with a selectivity of C2H2 (49%). Increase in power increased the conversion of methane while increase in pressure and/or inlet gas flow rate decreased it. Also, the results of the plasma-catalyst model were compared with those of plasma alone (without catalyst). It showed that presence of the catalyst inside the plasma increases the selectivity and yield of acetylene, while it deceases the selectivity and yield of hydrogen. Also, the density of radical CH3 in the plasma phase increased in the presence of catalyst, while CH2 and CH densities decreased with that