Influence of Small Amounts of Additives on Gas Hold-Up, Bubble Size, and Interfacial Area

Abstract

The gas-liquid interfacial area, which is determined by the gas hold-up and the Sauter mean bubble diameter, determines the production rate in many industrial processes. The effect of additives on this interfacial area is, especially in multiphase systems (gas-liquid-solid, gasliquid-liquid), often not understood. The addition of a third phase can cause the gas-liquid system to become completely opaque, which means that conventional techniques to study the interfacial area cannot be used. For this reason ultrasonic spectroscopy was used in this work to study the interfacial area and the bubble size distribution in these systems. The influence of different additives on the interfacial area was studied in a stirred vessel and in a bubble column under coalescing and noncoalescing conditions. It was found that the addition of toluene to a noncoalescing electrolyte system decreased the interfacial area to a large extent by turning it into a coalescing system, due to the interaction between gas bubbles and liquid organic droplets. Furthermore, around the toluene solubility concentration, both the gas hold-up (measured using an electric conductivity technique) and the interfacial area increased to values similar to those observed in noncoalescing systems. The cause of this remarkable phenomenon lies probably in the presence of a small toluene layer around the gas bubbles, which can be formed beyond the solubility point. This layer is absent at concentrations below the solubility limit and a large surface tension gradient exists between those two situations, which can be responsible for the sharp change in coalescence behavior.

Gas Absorption in Stirred Gas-Liquid-Liquid Systems: Effect of Transferred Solute Solubility and Oil Phase Spreading Characteristics

“…The specific area lack of sensitivity to organic holdup agrees with data obtained by Cents et al (2005) in a bubble column, both for spreading and non-spreading Das et al (1985), who found specific area to initially increase as toluene (spreading) holdup increased, go through a maximum at around 10% holdup, and then decrease, leading to depression of a at high holdup of toluene. Correia et al (2010) also found significant variation of specific interfacial area with holdup of a non-spreading organic phase.…”

Chemical Reaction Effect upon Gas–Liquid Interfacial Area in a Bubble Column Reactor

“…The gas hold-up increases slighter than the Sauter mean diameter behaviour, previously commented, and this fact explains the behaviour shown in Figure 6 for interfacial area. In the analysis of the gas flow-rate influence upon gas-liquid interfacial area, the higher values correspond to high gas flow-rates, and this behaviour is in agreement with the most common behaviour found in literature [26,27]. An increase in gas flow-rate produces large bubbles (see Figure 4), but also a high gas hold-up.…”

Hydrodynamics of gas-agitated liquid-liquid extraction columns

“…Vedaiyan et al (41) proposed an empirical correlation for the calculation of the Sauter drop diametar, given by: [18] where: u 0 -superficial velocity of the dispersed phase at the nozlle, d 0 -diameter of the nozlle of the distributor of dispersed phase. The influence of different additives (1-octanol; dodecane, and toluene) on the interfacial area was studied in a stirred vessel and in a bubble column under coalescing and noncoalescing conditions (42). The effect of additives on this interfacial area is often not undrestood, especially in multiphase systems (gas-liquid-solid, gas-liquid-liquid).…”