Mass transfer study on catalytic structured packings for reactive separations

This paper presents the results of a study carried out to examine the effective mass transfer area of the modular catalytic structured packing Katapak-SP. Information has been gathered by using the chemical absorption method and monitoring the composition profiles along the packed bed. Liquid load ranged between 5 and 27 m3/(m2h). A procedure was developed taking into account the complex geometry of the packing. The use of both volumetric mass transfer coefficients correlations from the literature and data from own measurements, allowed chosing the proper operating conditions. A simple model to calculate the effective area is presented. The model is based on the packing geometry and the liquid flows distribution within the hybrid structure of the packin

Effective mass transfer area of modular catalytic structured packings

This paper presents the results of a study carried out to examine the effective mass transfer area of the modular catalytic structured packing Katapak-SP. Information has been gathered by using the chemical absorption method and monitoring the composition profiles along the packed bed. Liquid load ranged between 5 and 27 m3/(m2h). A procedure was developed taking into account the complex geometry of the packing. The use of both volumetric mass transfer coefficients correlations from the literature and data from own measurements, allowed chosing the proper operating conditions. A simple model to calculate the effective area is presented. The model is based on the packing geometry and the liquid flows distribution within the hybrid structure of the packing

Production of a green multi-purpose fuel by reactive distillation

Dimethyl ether (DME) is receiving growing attention as a promising alternative and multipurpose green fuel. World production today is primarily by means of methanol dehydration using solid acid catalysts in a fixed bed reactor followed by ordinary distillation columns. In this study, the continuous production via a single reactive distillation (RD) column is studied experimentally in a pilot-scale plant. Kinetics of liquid dehydration of methanol over the sulphonic resin Amberlyst 35 is also studied, using both a batch reactor and a tubular fixed-bed reactor in a temperature range of 100-140°C and a pressure up to 50 bar. The experimental kinetic data are described well by the Eley-Rideal mechanism, and the kinetic parameters are incorporated into a rate-based RD model implemented in the simulation environment Aspen Custom Modeler® (ACM®). The pilot-scale RD experimental results support the feasibility and benefits of the DME synthesis by RD process and are used to validate the predictive RD model. The validated model can be used for future sensitivity analyses and process optimization studies as well as benchmarking compared to the state of the art technology

Effect of Composition-dependent Viscosity of Liquids on the Performance of Micro-mixers

The process of laminar mixing in a T-shaped micro-device is studied by direct numerical simulation for a model binary mixture, composed of two liquids having the same density and the same viscosity, yet presenting a strong fluidity of mixing effect, i.e. the viscosity of the mixture is a function of its composition. In particular, we consider the case where the viscosity of the mixture is up to three times larger than that of the pure liquids, with the maximum viscosity corresponding to either a 50 %-50 % (type 1 mixture), or a 25 %-75 % composition (type 2 mixture), to better emulate the behavior of real mixtures. The results are compared to the case with no fluidity of mixing effects (type 0 mixture), which has been largely investigated previously. In this latter case, the inlet streams remain separated up to a critical Reynolds number, corresponding to a strong increase of the degree of mixing. This transition is also characterized by a symmetry breaking, from a vortex flow regime, with a double mirror symmetry, to an engulfment flow regime, with a point central symmetry. When the fluid mixture has a larger viscosity than that of its pure components, a viscous layer forms at the confluence of the inlet flows, which tends to keep the two streams separated. Therefore, in this case, one would expect that the onset of the engulfment regime should be shifted to larger Reynolds numbers, in comparison with type 0 mixtures, with no sudden increase of the degree of mixing. Although this is what happens for symmetric, type 1 mixtures, for type 2 mixtures we unexpectedly find that, due to the lack of symmetry of the mixture rheology, the transition from vortex to engulfment regime, although occurring at larger Re, occurs suddenly, corresponding to a sharp increase of the degree of mixing

Mixing enhancement due to time periodic flows in a T-shaped micro-mixer

A Direct Numerical Simulation of the mixing process between two streams having the same flow rate in a T-shaped micro-device indicates that for a certain range of Reynolds numbers, Re, the flow regime might be unsteady, with time-periodic structures. Using a rectangular cross section with a 3:2 aspect ratio at the outlet and assuming fully developed flow at the inlet, pulsating flows are observed when 230<410; for example, when Re= 360, the time periodic structures were characterized by a Strouhal number, St 0.25, in good agreement with recent experimental results. Predictably, these pulsating flows strongly enhance the degree of mixing, that can be as large as twice the one that is measured in the steady engulfment regime. Then, when we increase the Reynolds number beyond the pulsating range, the flow is no more unsteady, with a consequent reduction of the mixing efficiency. In addition, we also observe that for our investigated geometry the unsteady, periodic behavior does not occur when the inlet flow profiles are blunt and not fully developed

Innovative LOPA-based methodology for the safety assessment of chemical plants

The aim of the present work was the development and application of a methodology for the safety assessment of chemical plants based on LOPA (Layer of Protection Analysis) techniques. The approach integrates the use of consolidate hazard identification techniques (HazOp) and the adoption of quantitative literature models for consequence assessment (e.g., integral models) into the LOPA framework, allowing to limit the role played by expert judgment in the evaluation in order to reduce the causes of uncertainty in the results. Furthermore, a systematic and quantitative assessment of safety measures contribution to the reduction of plant residual risk was included in the analysis. In order to apply the methodology, a case study was defined taking into account an actual industrial facility. The results obtained allowed demonstrating the potentialities of the method

Editorial

This special issue of Chemical Engineering Research and Design features selected papers from the international conference on Distillation & Absorption held in Friedrichshafenon 14–17 September 2014. The conference was organised byDECHEMA and ProcessNet’s Subject Division on Fluid Separations on behalf of the European Federation of Chemical Engineering (EFCE) and its Working Party on Fluid Separations.The first conference in this series took place in Brighton in the UK in 1960. The conferences are now held every 4 years, last in Eindhoven in 2010, and showcase the newest findings and research in distillation and absorption technology

Mixing of binary fluids with composition-dependent viscosity in a T-shaped micro-device

The process of laminar mixing in a T-shaped micro-device is studied by direct numerical simulation for a model binary mixture, composed of two fluids having the same density and the same viscosity, yet presenting a strong fluidity of mixing effect, i.e. the viscosity of the mixture is a function of its composition. In all cases, the inlet streams remain separated up to a critical Reynolds number, corresponding to the transition from a vortex flow regime, with a double mirror symmetry, to an engulfment flow regime, with a point central symmetry. In the case of a positive fluidity of mixing, the onset of the engulfment regime is accompanied by a sharp increase of the degree of mixing, with the critical Re decreasing as the fluidity of mixing increases. On the contrary, when the fluid mixture has a larger viscosity than that of its pure components, a viscous layer forms at the confluence of the inlet flows, which tends to keep the two streams separated. Therefore, in this case, no sudden increase of the degree of mixing is observed at the onset of the engulfment regime

Absorption of n-butyl acetate from tannery air emissions by waste vegetable oil/water emulsions

Tanning industries emit a huge quantity of Volatile Organic Compounds (VOCs), including hydrophilic and hydrophobic solvents. In this study, vegetable oil/water emulsions with 2 and 5 vol% of corn oil (O) or waste cooking oil (WCO) were prepared. Their potential as absorbents of n-butyl acetate (BA), in place of water, was investigated to increase the efficiency of tannery wet scrubbers. BA was selected as a representative component of hydrophobic VOC emissions derived from leather finishing processes. Static and dynamic absorption tests were performed with a BA concentration of 500 ppmv (2.6 g/m3 ) and a flowrate of 3.0 L/min to evaluate Henry’s law constant, absorption efficiency, absorption capacity, and saturation time of the various investigated absorbents. The feasibility of the absorbent regeneration was also studied by hot stripping with nitrogen. The results showed that Henry’s constant of BA in oil/surfactant/water or oil/water emulsions (5 vol% oil), regardless of the oil used, were significantly lower than those in water (3.6 versus 15.9 atm), and BA absorption capacity (0.84 g/L) was four times higher than the value in water. The presence of the surfactant (0.2–0.8 vol%) contributed to improving the oil/water emulsions stability without having a significant effect on BA absorption capacity. Almost complete BA desorption from the saturated emulsions was obtained by flowing hot N2 at 80◦C, demonstrating the absorbent regeneration’s feasibility followed by recovery and reuse. Therefore, the oil/water emulsions containing 5 vol% of WCO are efficient and sustainable absorbents of BA, with potential use in VOC emission treatment systems