Detection of Multiple Blockages in Parallelized Microreactors

In a plant consisting of parallelized microreactors (MRs), the product quality is lowered because of a lack of flow uniformity among them when blockage occurs. It is not practical to install sensors in every MR from the viewpoint of cost when detecting the blocked MRs. In the previous study, the multiple blockage detection (MBD) method using a small number of sensors was proposed, but its performance became low when the number of sensors decreased. Here, the conventional algorithm for MBD is improved by considering the process behavior on blockage occurrence, and the effectiveness of the improved algorithm is demonstrated through a numerical case study. The effects of flow distributor types and sensor types on the MBD performance are numerically investigated.     

Effect of Different Cosolvents on Transesterification of Waste Cooking Oil in a Microreactor

Biodiesel was prepared from waste cooking oil combined with methanol. The process was performed via transesterification in a microreactor using kettle limescale as a heterogeneous catalyst and various cosolvents under different conditions. n‐Hexane and tetrahydrofuran were selected as cosolvents to investigate fatty acid methyl esters (FAMEs). To optimize the reaction conditions, the main parameters affecting FAME% including reaction temperature, catalyst concentration, oil‐to‐methanol volumetric ratio, and cosolvent‐to‐methanol volumetric ratio were studied via response surface methodology. Under optimal reaction conditions and in the presence of the cosolvents n‐hexane and tetrahydrofuran, high FAME purities were achieved. Considering the experimental results, the limescale catalyst is a unique material, and the cosolvent method can reduce significantly the reaction time and biodiesel production cost.     

Integrated UV-based photo microreactor-distillation technology toward process intensification of continuous ultra-high-purity electronic-grade silicon tetrachloride manufacture

Ultra-high-purity silicon tetrachloride (SiCl₄) is demanded as an electronic-grade chemical to meet the stringent requirements of the rapidly developing semiconductor industry. The high requirement for ultra-high-purity SiCl₄ has created the need for a high-efficient process for reducing energy consumption as well as satisfying product quality. In this paper, a mass of production technology of ultra-high-purity SiCl₄ was successfully developed through chlorination reaction in the ultraviolet (UV)-based photo microreactor coupled with the distillation process. The influences of key operational parameters, including temperature, pressure, UV wavelength and light intensity on the product quality, especially for hydrogen-containing impurities, were quantified by the infrared transmittance of Fourier transform infrared spectroscopy (FT-IR) at 2185 cm⁻¹ and 2160 cm⁻¹ indicating that characteristic vibrational modes of SiH bonds, as well as the operating conditions of distillation were also investigated as key factors for metal impurities removing. The advanced intensification of SiCl₄ manufactured by the integration of photo microreactor and distillation achieves the products with superior specifications higher than the standard commercial products.     

Effects of microreactor wall heat conduction on the reforming process of methane

In this paper, the effect of wall conduction of an autothermal tubular methane microreformer is investigated numerically. It is found that the axial wall conduction can strongly influence the performance of the microreactor and should not be neglected without a careful a priori investigation of its impact. By increasing the wall thermal conductivity, the maximum wall surface temperature is decreased. Due to the complex exothermic–endothermic nature of the chemistry of reforming, the axial variation of the wall temperature is not monotonic. Methane conversion and hydrogen yield are strongly dependent on the wall inner surface temperature, hence the heat conduction through the channel wall. The equivalence ratio and the wall thickness also significantly affect the reforming effectiveness and must be carefully considered in reactor optimization. Furthermore, it is found that exothermic oxidation reaction mechanisms, especially partial oxidation, are responsible for syngas (hydrogen and carbon monoxide) production near the inlet. Farther downstream, in the oxygen deficient region, endothermic steam reforming is the main hydrogen producing mechanism. By increasing the thermal conductivity, steam reforming becomes stronger and partial oxidation becomes weaker. For all investigated inlet conditions, the highest hydrogen yield is obtained for no or very low conductive walls.     

Corrosion resistant and adsorbent plasma polymerized thin film

Adsorbent and corrosion resistant films are useful for sensor development. Therefore, the aim of this work is the production and characterization of plasma polymerized fluorinated organic ether thin films for sensor development. The polymerized reactant was methyl nonafluoro(iso)butyl ether. Infrared Spectroscopy showed fluorinated species and eventually CO but CH_n is a minor species. Contact angle measurements indicated that the film is hydrophobic and organophilic but oleophobic. Optical microscopy reveals not only a good adherence on metals and acrylic but also resistance for organic solvents, acid and basic aqueous solution exposure. Double layer and intermixing are possible and might lead to island formation. Quartz Crystal Microbalance showed that 2-propanol permeates the film but there is no sensitivity to n-hexane. The microreactor manufactured using a 73 cm long microchannel can retain approximately 9 × 10⁻⁴ g/cm² of 2-propanol in vapor phase. Therefore, the film is a good candidate for preconcentration of volatile organic compounds even in corrosive environment.     

Direct conversion of syngas to DME as a green fuel in a high pressure microreactor: Influence of slurry solid content on characteristics and reactivity of washcoated CuO–ZnO–Al2O3/HZSM-5 nanocatalyst

Microchannels of a stainless steel microreactor were successfully washcoated with slurry of Cu–ZnO–Al₂O₃/HZSM-5 (CZAZ) nanocatalyst with different concentrations (10, 20 and 30 wt.%). The properties of nanocatalyst and the washcoated microchannels were investigated by XRD, FESEM, N₂ physisorption, FTIR, EDX-Dot mapping and EDX-Line mapping analysis. The best adherence was observed for 20 wt.% catalyst which has a uniform coating, almost no cracks and homogenous dispersion of copper and zinc. Trend of weight gain during 10 soaks in catalyst slurry was very slow for 10 wt.% but faster for 20 and 30 wt.%. Low amount of weight gain was observed for the last soaks of catalyst slurry in the case of 30 wt.% washcoating. The performance of microreactor with different slurry concentrations were evaluated in direct synthesis of DME at 200–300 °C, 60–150 cm³/min and 40 bar. Regardless of slurry concentration, the microreactor exhibited a better reactivity in comparison to fixed-bed reactor performance. Among three different slurry concentrations, 20 wt.% catalyst slurry revealed the best reactivity in direct DME synthesis. The reduction in reactor performance at higher flow rates was significant in the fixed-bed reactor while microreactor, particularly 20 wt.% washcoated channels, revealed less drastic reduction.     

Bromination of Aromatic Compounds using Bromine in a Microreactor

2,4,5‐Trifluorobromobenzene is a valuable intermediate with important application in the synthesis of biologically active peptides and fluorescent reagents. A continuous‐flow system has been successfully developed for the synthesis of 2,4,5‐trifluorobromobenzene in a microreactor using FeBr₃ as a catalyst, which is steadily generated in situ from the reaction of Br₂ and Fe. The procedure is efficient and easy‐to‐handle, and 2,4,5‐trifluorobromobenzene can be obtained within minutes in high yields.     

Monolithiation of 5,5′‐Dibromo‐2,2′‐bithiophene Using Flow Microreactors: Mechanistic Implications and Synthetic Applications

The lithiation of 5,5′‐dibromo‐2,2′‐bithiophene with one equivalent of an alkyllithium such as n‐BuLi or s‐BuLi was studied by varying the residence time in flow microreactors. With a short residence time, the product 2,2′‐bithiophene (3) derived from dilithiation was obtained preferentially and a significant amount of the starting material 5,5′‐dibromo‐2,2′‐bithiophene remained unchanged. An increase in the residence time caused a higher yield of the product 5‐bromo‐2,2′‐bithiophene derived from monolithiation with expense in the yields of 2,2′‐bithiophene and 5,5′‐dibromo‐2,2′‐bithiophene. The lithiation using MeLi gave the product 5‐bromo‐2,2′‐bithiophene preferentially even with a very short residence time.     

Mass transfer simulation of biodiesel synthesis in microreactors

A coupled nonlinear mathematical model for the mass transfer of the species involved in the transesterification reaction between soybean oil and methanol in a parallel plates geometry microreactor is presented. The set of partial differential equations that governs the concentration profile of these species were obtained from the general mass balance equation for the case of isothermal flow and steady state with constant physical properties. The velocity profile was obtained from the Navier-Stokes equations assuming fully developed stratified laminar flow for two immiscible Newtonian fluids, with a plane interface between them, based on experimental observation of this flow pattern. The second order kinetic equations for the species were developed assuming homogeneous and reversible chemical reactions and these equations were written as source terms in the main equations. The mathematical model was solved using the hybrid method known as Generalized Integral Transform Technique (GITT). The simulation results were critically compared with those obtained by using the COMSOL multiphysics platform, showing a good agreement between the hybrid and fully numerical simulations. The effects of governing parameters such as residence time, temperature and microreactor dimensions were investigated. It was observed that higher triglycerides conversion rates occurred at higher temperatures and residence times and lower microreactor depths.     

Alcohol ethoxylation kinetics: Proton transfer influence on product distribution in microchannels

The influence of the reactor type on the product distribution of the base catalyzed ethoxylation of fatty alcohols was studied.Commonly, proton exchange equilibrium is assumed when modeling this reaction to calculate the product distribution. The model is applicable for ethoxylates produced in semibatch, but cannot explain the products obtained from a continuous microstructured reactor.In this work, a non-equilibrium model is proposed to explain the observed distributions. The model is better suited to fit the distribution curves, and was used to determine the kinetic parameters of this reaction.For the propagation reaction, an activation energy E_A,P = 74 kJ mol⁻¹ was found, which is in good agreement to literature data. For the proton transfer, activation energies in the range of 56 kJ mol⁻¹ to 68 kJ mol⁻¹ were observed.