Photodegradation of methylene blue dye by the UV/H2O2 and UV/acetone oxidation processes

The photodegradation of methylene blue (MB) dye in aqueous solutions was investigated using a laboratory-scale UV lamp in the presence of hydrogen peroxide (H2O2). Different initial concentrations of dyes (10, 20, 30, 40 ppm) were investigated using different doses of H2O2. Substantial decolorization of the dye was reached using UV/H2O2, where neither UV nor H2O2 alone was appreciably able to decolorize any of the dyes. The optimum dose of H2O2 increased with the increase of the initial concentration of the dye. The experimental decoloration kinetics data followed the pseudo-first-order reaction model. The time of decoloration increased with an increase in the initial dye concentration. The effect of the presence of photosensitized material such as acetone on the decoloration rate of the MB dye was also examined. Increasing acetone concentration shortened the time needed to completely decolorize MB solutions. The oxidation role of hydroxyl-free radicals was evaluated using sodium carbonate

Studies of microstructured falling film reactor using Eddy diffusivity concepts

Introduction. This work introduces a model for the absorption of CO2 in a falling film microreactor that incorporates staggered herringbone structures. The effect of the herringbone structures was incorporated into the model via a position dependent eddy diffusivity obtained from turbulent theory concepts. Results from the model are in good agreement with experiments

CONTINOUS MULTI-PHASE FLOW REACTOR FOR SMALL AND LARGE FLOW CAPACITIES THAN L/MIN

Multiphase flow processing in flow reactors holds great promises for diverse applications in fine chemicals and materials synthesis primarily due to its precise control over the flow, mixing and reaction inside or between each phase. Even though, flow reactors have shown superior performance, so far batch reactors still dominating the landscape for industrial manufacturing in the pharmaceutical and fine chemicals. Nonetheless, the base of switching to continuous flow reactors is making its way. Recently, a good article has been published which summaries the complexity of introducing new disruptive technology and why flow reactors are taking so much time to make it industrial scale manufacturing. (1). One of these factors is the need to reduce the investment and technological risks of scale-up which we address here. In this paper, we present an effort into developing a scale-up methodology to smoothly bridge the gap between continuous flow laboratory reactors and those for industrial scale manufacturing. The methodology relies on the concept of numbering-up, placing multiple reaction channels in parallel to increase the flow capacity rather than scaling-up the reaction channel dimensions. The key to this methodology is the flow distribution to ensure equal flow rate and temperature to all parallel reaction channels (2). The second key is the reactor assembly and design that is suitable for industrial scale fabrication and manufacturing. A case study to demonstrate this reactor and methodology will be presented. First, the flow uniformity for segmented gas-liquid flow will be demonstrated in a hydrodynamic study. Two criteria for obtaining uniform segmented flow distribution in the system are found as a proper pressure balance in the system (i.e., a high ratio of pressure drop in the barrier channels to that in the reaction microchannel) and the avoidance of bubble coalescence. Second, the gas-liquid segmented flow distribution performance of the reactor is evaluated using fluid pairs with different liquid phase viscosity and surface tension properties. Third, the reactor is tested using a hydrogenation reaction as an industrially relevant model reaction. Finally, the scalability of this reactor design is demonstrated via combining two stacks of such multi-layer microreactors the liquid throughput of which is possible to reach about 1 ton per day. References 1. Roberge M.D. “The complexity of technology implementation: flow versus batch processing”. Chimica Oggi-Chemistry Today. vol. 30(5) 2. M. Al-Rawashdeh, F. Yu, T. A. Nijhuis, E. V. Rebrov, V. Hessel and J. C. Schouten. “Numbered-up gas-liquid micro/milli channels reactor with modular flow distributor”, Chem. Eng. J., 207-208, pp.645-655, 201

Pseudo 3-D simulation of a falling film microreactor based on realistic channel and film profiles

A falling film microreactor has demonstrated in the past high potential for sustainable chemical processes, e.g. by better use of resources (selectivity), enabling direct routes (saving of waste), or smaller reactor footprint (space-time yield). Due to the extremely high liquid based specific area (up to ) it is especially equipped to carry out fast exothermic and mass transfer limited reactions. However, to maximize the process intensification in the falling film microreactor there is a need to characterize and investigate the design parameters of the reactor. In general, the major rate limiting steps occur on the liquid side. Therefore a realistic description of the liquid film is needed which requires the use of a 3-D reactor model. In the current study we present a so-called pseudo 3-D computational fluid dynamic (CFD) model. Based on the realistic channel geometry profiles we compute liquid menisci, flow velocities, species transport, and reactions. The reactor model was developed and validated experimentally by the absorption of CO2 in NaOH aqueous solution. This 3-D model allows investigating the effects of channel fabrication precision, liquid flow distribution, gas chamber height, and hydrophilic–hydrophobic plate material. Result shows that fabrication imprecisions of the investigated microchannels by 11% in channel width and 6% in channel depth has only a 2% impact on the reaction conversion. Moreover we show that a liquid flow mal distribution, in the parallel microchannels assembled on plate, with a relative standard deviation of 0.37 lowers the reaction conversion by about 2%. A reduction of gas chamber height slightly improves the conversion and gas phase mass transfer limitation can be overcome. Moreover the material of the reactor plate has to provide sufficient wetability for the liquid falling film