Mass-Transfer Properties of Microbubbles. 1. Experimental Studies

Abstract

Synthesis-gas fermentations have typically been gas-to-liquid mass-transfer-limited due to low solubilities of the gaseous substrates. A potential method to enhance mass-transfer rates is to sparge with microbubble dispersions. Mass-transfer coefficients for microbubble dispersions were measured in a bubble column. Oxygen microbubbles were formed in a dilute Tween 20 solution using a spinning disk apparatus. Axial dispersion coefficients measured for the bubble column ranged from 1.5 to 7.2 cm2/s and were essentially independent of flow rate. A laser-diffraction technique was used to determine the interfacial area per unit gas volume, a. The mass-transfer coefficient, KL, was determined by fitting a plug-flow model to the experimental, steady-state, liquid-phase oxygen-concentration profile. The KL values ranged from 2.9 x 10(-5) to 2.2 x 10(-4) m/s. Volumetric mass-transfer coefficients, KLa, for microbubbles with an average initial diameter of 60 microns ranged from 200 to 1800 h-1. Enhancement of mass transfer using microbubbles was demonstrated for a synthesis-gas fermentation. Butyribacterium methylotrophicum was grown in a continuous, stirred-tank reactor using a tangential filter for total cell recycle. The fermentation KLa values were 14 h-1 for conventional gas sparging through a stainless steel frit and 91 h-1 for microbubble sparging. The Power number of the microbubble generator was determined to be 0.036. Using this value, an incremental power-to-volume ratio to produce microbubbles for a B. methylotrophicum fermentation was estimated to be 0.01 kW/m3 of fermentation capacity.

Microbubble fermentation of recombinant Pichia pastoris for human serum albumin production

“…Weber (2003) used microbubble dispersion to cultivate Trichoderma reesei for cellulose enzyme production. In an anaerobic fermentation, Bredwell and Worden (1998) applied the MBD to increase the mass transfer of synthesis gas to produce ethanol and butanol.…”

A review of conversion processes for bioethanol production with a focus on syngas fermentation

“…Klasson et al (1990a) used two STRs in series and reported a 30 fold increase in ethanol productivity using C. ljungdahlii. Bredwell and Worden (1998) showed that the use of a microsparger in a STR for production of acetate, ethanol and butyrate by Butyribacterium methylotrophicum increased the mass transfer by six times with 50% of the flow rate used without a microsparger. The highest ethanol concentration of 48 g/L was produced in a continuous syngas fermentation in a CSTR with cell recycle (Phillips et al, 1993).…”

“…Mass transfer characteristics of various reactor configurations have compared by many researchers (Bredwell and Worden, 1998;Cowger et al, 1992;Jones, 2007;Klasson et al, 1990b;Klasson et al, 1991;Klasson et al, 1993a;Munasinghe and Khanal, 2010b;Munasinghe and Khanal, 2014;Orgill et al, 2013;Riggs and Heindel, 2006;Shen et al, 2014a;Yasin et al, 2014). In a STR, the mass transfer coefficient can be increased by increasing 268-280.…”

Rheology and convective heat transfer of colloidal gas aphrons in horizontal mini-channels

“…Most applications of colloidal gas aphrons take advantage of (i) their large interfacial area, (ii) the adsorption of particles at the microbubble interfaces, and (iii) their stability for enhanced mass transfer [3]. Possible applications include (1) separation, (2) oil recovery, (3) firefighting, (4) fermentation and bioreactors, (5) material synthesis, and wherever macroscopic foams are currently being used.…”

“…They studied the liquid drainage rate in CGA dispersion and the bubble rise velocity. Bredwell and Worden [3] estimated the shell thickness to be 200-300 nm for nonionic surfactant Tween-20, based on the study of gas diffusion from the CGA bubble to the liquid bulk, assuming that the mass transfer is limited by the rate of diffusion across the shell. More recently, Jauregi et al [26] employed freeze fracture with TEM and X-ray diffraction to study the structure of the soapy shell.…”