Gas–Liquid Flow and Mass Transfer in an Advanced-Flow Reactor

Abstract

Hydrodynamics and mass transfer of gas−liquid flow are explored under ambient conditions in an Advanced-Flow Reactor (AFR), an emerging commercial system designed for continuous manufacture. Carbon dioxide/water is the model system used in this study for a range of flow rates for gas and liquid of 5.6−103 mL/min and 10−80 mL/min, respectively. Bubble size distribution, gas holdup, specific interfacial area, pressure drop, and mass transfer coefficients are determined from flow visualization experiments and compared with conventional gas−liquid contactors. These variables are mainly influenced by the inlet flow rates and inlet composition. Average bubble sizes (d B ) of 0.9−3.8 mm, gas holdup (ε G ) of 0.04−0.68, specific interfacial areas (a) of 160−1300 m 2 /m 3 , and overall mass transfer coefficients (k L a) of 0.2−3 s −1 were obtained for the vertical orientation of the AFR. Although effect of gravity is present for this system, no significant effect on the hydrodynamic properties was observed. The measured pressure drop for vertical orientation (3.6−53.4 kPa) was used to estimate power consumption, which is used as a metric to compare mass transfer efficiency among different gas−liquid contactors. A power law relationship was obtained for the overall mass transfer coefficients in terms of power input and gas holdup, given by k L a = 0.101P w 0.443 ε G 0.459 . The design of the AFR with a series of heart-shaped confined sections with obstacles enhances continuous breakup and coalescence of bubbles providing interfacial areas and mass transfer coefficients 1 order of magnitude larger than other gas−liquid contactors, such as bubble columns (50−600 m 2 /m 3 ; 0.005−0.24 s −1 ) and spray columns (75−170 m 2 /m 3 ; 0.015−0.022 s −1 ), and 1 order of magnitude smaller than gas−liquid microchannels (3400−9000 m 2 /m 3 ; 0.3−21 s −1 ) or falling film reactors (20,000 m 2 /m 3 ).

Beyond Organometallic Flow Chemistry: The Principles Behind the Use of Continuous-Flow Reactors for Synthesis

“…203 Overall volumetric mass transfer coefficients (kLa) in this device range between 0.1-10 s -1 , which can be compared with those values obtained in a microreactor. 204 This concept has been used to scale oxidation reactions, such as ozonolysis 205 and alcohol oxidations with bleach. 206 For the latter, the oxidation of 1-phenylethanol could be scaled from 0.0064 g/min in a microreactor to a Low Flow reactor (0.37 g/min) and Advanced Flow Reactor (4.08 g/min).…”

Porous polypropylene membrane contactors for dehumidification of gases

“…Gas-liquid membrane contactors where the liquid and gas phases are separated by a semipermeable membrane (especially hollow fiber membranes) were suggested as an alternative technology for overcoming drawbacks of direct gas-liquid contactors [10][11][12]. Moreover, utilization of membrane contactors allows to increase interfacial contact area over 2000 m 2 /m 3 compared to 50 -600 m 2 /m 3 typical for classic contact devices [13]. Membrane contactors are generally divided into two groups: non-porous contactors (usually having an asymmetric structure with selective layer) and porous contactors.…”

Microreactor Mixing-Unit Design for Fast Liquid-Liquid Reactions

“…Previous work [11][12][13][14][15][16][17] studied the effects of using passive micromixing structures to increase the mass transfer rate between two immiscible phases in flow ranges that would have otherwise been in the slug flow regime for a similar-sized capillary reactor. A micromixer-based reactor was shown to be well suited for fast liquid-liquid reactions [14] (i.e., mass or heat transfer limited with reaction times in the millisecond to second range).…”