Gas dispersion in highly viscous liquids using a SMX static mixer
Multi-scale and/or multi-disciplinary approach to process-product innovation
Innovative Process Equipment-Operation Design & Analysis (T3-10)
Keywords: Gas dispersion, mass transfer, laminar, static mixer, dynamic mixer
The dispersion of gas into liquids is a common unit operation in the chemical industry. However, in cases where the liquids have a high viscosity, e.g. the processing of foods like dairy products or the production of foams made from polymers, gas dispersion is a difficult mixing task due to the high viscosity ratio of the continuous and dispersed phase and the small diffusion coefficients of the gas dissolved in the liquid. The SMX mixer is among the most applicable mixers for this difficult mixing task due to its internal structure, which consists of crossed blades resulting in uniform energy dissipation and a flow field with extensional components favorable for bubble break-up.
In the presented study, a SMX static mixer was used to disperse gas into highly viscous liquids. The flow was kept laminar in all experiments. The effects of the operating condi-tions such as energy input and gas phase mass fraction as well as the length of the mixer and the rheology of the liquid phase were investigated. The measurement of the bubble size distribution was based on photographs of the bubbly flow that were taken through a transparent section after the static mixer.
Different silicone oils with varying viscosities and a polymer melt were used as the liquid phase, helium and nitrogen as the gas phase. Because the two gases show a noticeable solubility in the liquid phase, the break-up of the bubbles is associated with the absorption of the gas into the liquid. The mass fraction of gas in the liquid phase was determined by a mass balance of the gas. The results are presented in terms of the bubble size distribution and the mass fraction of the gas dissolved in the liquid.
Using an average difference of the gas mass fraction before and after mixing, the mass transfer coefficient can be calculated. The static mixers studied show mass transfer coef-ficients that are several-fold higher than those of agitated vessels found in the literature. Compared to these dynamic mixers, the energy input into the SMX static mixers is trans-formed more efficiently into liquid phase mixing and the growth of the interfacial area due to bubble break-up.
Presented Thursday 20, 11:00 to 11:20, in session Innovative Process Equipment-Operation Design & Analysis (T3-10).
