Chemical Engineering and Processing - Process Intensification最新文献

Liquid-liquid emulsions are used in various sectors, including food, health care, personal care, home care and nutrition. There is an increasing need for developing equipment and devices for producing emulsions with desired drop size distribution (DSD) in a continuous mode of operation to fulfil market demands. In this work, we experimentally investigated droplet size distributions of emulsions made using selected cavitation-based emulsion producing devices operated in a continuous mode. Emulsion production devices considered in this work are wet mill, Soldo cavitator, Dynaflow cavitator and different scales of vortex based hydrodynamic cavitation devices. The continuous emulsion production experiments were performed for generating 5 % rapeseed oil-in-water emulsions using different devices. Performance of different emulsion production devices based on energy efficiency of emulsification $\left(\eta \right)$, energy consumption per kilogram of emulsion $\left(E\right)$, interfacial area created per unit energy consumption ${\left(A_{net}\right)}_P$, Sauter mean diameter $\left(d_{32}\right)$, other characteristic diameters $\left(D10,D50,D90\right)$, and drop size distribution (DSD) was compared. Among all the devices, vortex based hydrodynamic cavitation (HC) devices showed excellent performance in terms of lower $d_{32}$ and DSD with low $E$ and high $\eta$. The smallest scale of vortex-based HC device exhibited the highest efficiency (∼0.16 % at $E$ = 2.6 kJ/kg) over the entire range of $E$ compared to the other devices considered in this study. The presented data and analysis will be useful for selection of emulsion producing devices for desired emulsion characteristics and production capacity.

Magnetically agitated miniaturised continuous stirred tank reactors (mCSTRs) are an attractive platform for the intensification of chemical reactions involving solids by combining active stirring and intensified heat and mass transfer due to their small dimensions. This work investigated the operation of mCSTRs at flowrates up to 60 ml/min (space time of 3 s per tank) as a means of increasing the throughput of fast reactions. Investigation of the residence time distribution under varying operational (flowrate, stirrer rotational speed) and reactor geometrical (stirred volume, stir bar size) parameters, showed deviation from the ideal CSTR behaviour at increasing flowrates, which could be mitigated by keeping the stir bar length close to the tank diameter, increasing stirrer rotational speed, and using larger tank sizes. Assembling mCSTRs into cascades did not amplify non-ideal behaviour and allowed narrowing the residence time distribution at high throughput. Various configurations of mCSTR cascades were evaluated for the synthesis of iron oxide nanoparticles (IONPs) via iron chloride co-precipitation with NaOH, demonstrating the importance of residence time distribution (RTD) control when increasing the throughput of nanoparticle production. Using a 5 × 3 ml mCSTR cascade for the core formation followed by a 5 × 3 ml mCSTR cascade for deagglomeration/stabilisation, the IONP flow synthesis was scaled successfully, producing high quality nanoparticles (7.3 $\pm$ 2 nm) at 60.5 ml/min (l/h scale).

Microbubbles play a crucial role in various industries due to their advantages, such as small diameter, stable phase interface, and large specific surface area. Consequently, microbubble generators have entered a period of development. Among various microbubble generators, the Venturi tube stands out for its simple structure and high foaming efficiency. However, it still faces drawbacks, such as significant variations in particle size. Therefore, a new microbubble generator that utilizes the Venturi tube is currently being investigated. The tail of Venturi tube is connected with Tesla valve. According to the number and position of Tesla valves, various structures are formed: single-segment, multi-segment, and multi-segment same-side or different-side Tesla valves. Various structural characteristics are compared using Fluent software, and the optimal structural dimensions are determined using the Response Surface Methodology (RSM). The results show that the symmetrical distribution on both sides of Tesla valve is the best, and the proportion of microbubbles can be increased to 90%. The optimal dimensions are found to be an inclination angle (α3) of 34°, an inclination length (L8) of 29 mm, and a displacement length (L9) of 0. The optimized new structure is tested, and the reliability of the simulation results is verified.

Environmentally friendly aqueous asymmetric supercapacitors are expected to exhibit excellent energy storage properties, stable performance, and facile production protocols. This study focused on the fabrication and characterisation of an asymmetric supercapacitor (ASC) with a commercial activated carbon (AC) negative electrode and Mn(OH)₂/Mn₃O₄ composite on carbon cloth (hCC) positive electrode. The Mn-based electrode was synthesised using a one-step electrodeposition process. The morphology and crystalline structure of the composite electrode were modified by varying the deposition time of the Mn(OH)₂/Mn₃O₄ nanostructures on carbon cloth substrate which greatly influence the electrochemical performance of the asymmetric systems. The best ASC used the AC electrode and a Mn(OH)₂/Mn₃O₄@hCC electrode prepared using electrodeposition over an optimised time of 3 h. It exhibited a remarkable specific energy density of 40.7 Wh kg⁻¹ at a power density of 100 W kg⁻¹. In addition, this ASC demonstrated stable long-term performance, retaining 88 % of its capacitance after 5000 charge–discharge cycles, showing its great application potential in the field of supercapacitors.

Saline effluents containing primarily sodium chloride (NaCl) and sodium sulfate (Na2SO4) are generated from common salt production, tannery CETPs, textiles industries, desalination rejects, etc. In this work, experimental studies have been conducted for parametric evaluation of crystallization techniques for selective isolation of Na2SO4 and NaCl from saline effluent. Three crystallization approaches, i.e., evaporation-crystallization, cooling-crystallization, and antisolvent-crystallization, are assessed through parametric studies. A representative saline solution generated from a salt refinery unit is considered for the study. Lab-scale experiments were performed to determine the optimum process conditions for each crystallization process, and their performance was evaluated by estimating the separation efficiency. Chemical, P-XRD, and TGA analyses were performed to characterize the product composition, purity, and hydration state. For selective Na2SO4 recovery, cooling crystallization, and antisolvent crystallization were found suitable over evaporation crystallization. Subsequently, integrated process variants for cooling crystallization and antisolvent crystallization-based separation were developed. A techno-economic assessment (TEA) was performed to compare integrated process variants for the recovery of salts (Na2SO4 and NaCl) and establish the prospective towards commercialization. The parametric evaluation and TEA shows that the combined crystallization technologies can be potential approach to recover added-value products from saline effluents promoting waste to wealth notion.

The present study explored the optimization of a reactive distillation column (RDC) for biodiesel production using supercritical transesterification (SCTE). The SCTE process at high pressure and temperature, is known for water-sensitive flexibility and catalyst-free operation, and has shown promising advantages in biodiesel production. The steady-state simulations were conducted using Aspen Plus, with two RDC configurations: RDC-1, employing a single feed of oil and methanol, and RDC-2, utilizing separate feeds. Surprisingly, high conversion rates were achieved at only 8.5 MPa pressure. The study aiming to identify an optimized RDC design, systematically examined the impact of design parameters such as reflux ratio, feed temperature, and the number of reactive stages on conversion and energy requirements. Internal column specifications and species flow through each stage were investigated to comprehend reaction and separation processes. Temperature analysis revealed that preheating to 380 °C significantly improved conversion and reduced reboiler heat duty. RDC-1, with 9 reactive stages, demonstrated greater conversion efficiency, while RDC-2, with 11 stages, exhibited better biodiesel separation. By optimizing reflux ratios, the study achieved remarkable conversions with enhanced methanol separation. Cost estimation revealed that RDC-1 promoted lower capital and operating costs, making it a preferred design and an efficient option for SCTE-based biodiesel production.

Methane pyrolysis (MP) is one of enabling technologies in the economy transition from fossil to renewable fuels. Although the technology has its undoubted advantages, the cost of producing hydrogen with MP is still higher than that using Steam Methane Reforming (SMR). Remote and contactless catalyst heating by microwaves can significantly intensify methane pyrolysis and reduce these costs. One of the catalysts that can be utilized in the microwave-assisted MP is the Fe/C catalyst. The current work presents a reference study of the MP kinetics on the dedicated Fe/C catalyst under conventional (non-microwave) heating. The kinetic data determined in this work are necessary for appropriate modelling and design of the microwave-assisted MP reactor. Experiments were carried out using thermogravimetric analysis coupled with gas chromatography. The reaction order with respect to methane and the activation energy were found to be 0.6, and 71 kJ/mol, respectively. The effects of CO₂ concentration and temperature on the regeneration of the catalyst were also demonstrated.

One way to overcome the inhibitory effects caused by ethanol on yeast cell growth is the use of extractive fermentation, whereby ethanol is removed from the fermentation broth as it is produced. The present work investigates ethanol removal from solution by vacuum-assisted gas stripping, which is a promising method for enhancing performance, compared to conventional gas stripping. Evaluation was made of the effects of carbon dioxide flow rate (ϕ_CO2), temperature (T), and pressure (P) on ethanol removal performance. Bench-scale assays were performed using a 2-L bubble column containing 10 % v/v ethanol solution, with monitoring of the gas and liquid phases by FT-MIR spectroscopy. The ethanol entrainment factor (F_E) increased with ϕ_CO2 and temperature, but decreased at higher pressure. Only ϕ_CO2 had significant and positive effects on the concentration factor (F_C) and selectivity (α_E/W), within the operating ranges of the variables studied. An ethanol removal model was obtained that provided an accurate description of the process behavior, with good agreement between the experimental and simulated data. In addition, the energy requirement for ethanol removal by vacuum-assisted gas stripping in the bioreactor was lower than for the conventional stripping process.

The principles of sustainable development require decarbonization of the chemical sector. An example of the implementation of this strategy is electrification of the Dry Reforming of Methane (DRM). In this work, five electricity-based DRM technologies targeting the chemistry (photocatalysis and plasma) and the heat supply (microwaves, Joule heating and induction heating) are analyzed and compared. The following issues are discussed for all technologies: feasibility of large-scale reactor design and operation, reactants conversion and syngas production rates, energy consumption/efficiency, coking, process economy and safety. On the short term, the Joule heating appears to be the most promising of the five technologies reviewed, due to its relative simplicity, high methane conversions and high electricity-to-heat efficiency.

The presence of carbon dioxide in combustion products is one of the main reasons for global warming. Supersonic separation is a modern, eco-friendly, and cost-efficient technology for capturing carbon dioxide. In this study, the physics of CO₂ condensation through a supersonic separator nozzle for purifying the flue gas mixture is modeled using a numerical programming method based on the finite volume AUSM scheme. A limiting maximum for condensation efficiency relative to the CO₂ content in the flue gas was demonstrated for fixed inlet conditions. The idea of enhancing the carrier gas heat capacity by hydrogen enriching for promoting droplet formation and condensation of CO₂ in the mixture is being studied for further increasing condensation efficiency. The analysis uses the Peng-Robinson equation of state formulation, the multi-diameter growth model appropriate for the Eulerian-Eulerian problem, and the nucleation model suitable for high-speed mixture flows. The results show that adding about 48 % molar fraction of hydrogen increases the growth of droplet and condensation efficiency about 1.3 and 1.5 times, respectively. This technique can significantly increase the separation efficiency in supersonic separators.