The effects of liquid phase rheology on the hydrodynamics of a gas–liquid bubble column reactor Amin Esmaeili, Christophe Guy, Jamal Chaouki n Department of Chemical Engineering, École Polytechnique de Montréal, P.O. Box 6079, St. C.V., Montreal, Que., Canada H3C 3A7 HIGHLIGHTS  The effect of liquid rheology on hydrodynamics of a bubble column reactor is studied.  A new approach based on the dynamic moduli is proposed to interpret the rheological effects.  Coalescing effects of highly viscous liquids can be suppressed in the presence of elasticity.  The elastic effects of non-Newtonian liquids increase the gas holdup.  Bubble chord length decreases when the elasticity of liquid dominates. article info Article history: Received 9 October 2014 Received in revised form 14 December 2014 Accepted 6 January 2015 Available online 9 March 2015 Keywords: Bubble column Rheology Hydrodynamics Pressure fluctuations Gas holdup Viscoelastic fluids abstract In this study, the effects of liquid phase rheology on the hydrodynamics of a pilot scale bubble column reactor is extensively investigated by applying various types of test liquids with different rheological characteristics as the operating fluids. Two fiber optic probes and several pressure transducers are used and different time-domain and frequency-domain analyses are applied to perform a comprehensive interpretation of the pressure signals and measure the hydrodynamic parameters of the gas phase. A new approach is proposed based on the dynamic moduli of viscoelastic solutions to better understand the simultaneous viscous and elastic effects. It was observed that the elasticity of the operating liquid reduced the average bubble chord length and increased the total gas holdup. The obtained results reveal that although the viscosity is more favorable for coalescence, the elasticity of the operating liquid can prevent bubble coalescence by showing a solid-like behavior at the interface of two bubbles. & 2015 Elsevier Ltd. All rights reserved. 1. Introduction Bubble column reactors have a wide range of applications in processes based on the contact between gas and liquid phases, such as the Fischer–Tropsch (FT) synthesis, the liquid phase methanol synthesis (LPMeOH) and the hydroconversion of heavy oils and petroleum residues (Shaikh and Al-Dahhan, 2007; Sheikhi et al., 2013; Wang et al., 2007). These reactors have received a great deal of attention from both academia and industry over the last few decades since they offer excellent heat and mass transfer performance, low operating and maintenance costs because of the absence of moving parts, and are easy to operate (Gandhi et al., 1999; Kantarci et al., 2005; Shah et al., 1982). With the dramatic increase in the world energy demand and the appearance of a new generation of feedstocks, gas–liquid contactors and in particular bubble column reactors have become increasingly important. Although many liquids in industrial pro- cesses are low molecular weight and Newtonian-like fluids, an increasing number of high molecular weight solutions with com- plex internal structure and non-Newtonian behavior are being used in the fields of enhanced oil recovery, wastewater treatment, polymerization processes, and the production of foods and phar- maceuticals. Bubble behavior as the key hydrodynamic factor in bubble column reactors can drastically change in the presence of non-Newtonian fluids. While research on bubble columns is mainly focused on Newtonian fluids, it is of fundamental impor- tance to understand the non-Newtonian effects on the behavior of bubbles and hydrodynamics. Generally, increasing the liquid phase viscosity has been shown to decrease the total gas holdup and hinder the formation and stability of a homogeneous bubble bed. This negative effect is mainly ascribed to the existence of drag forces enhancing bubble coalescence in the gas sparger zone (Ruzicka et al., 2003; Urseanu et al., 2003; Zahradnik et al., 1997). Schafer et al. (2002) pointed out that the turbulence in the liquid phase diminishes by increas- ing the viscosity and consequently, the liquid eddies obtain less Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ces Chemical Engineering Science http://dx.doi.org/10.1016/j.ces.2015.01.071 0009-2509/& 2015 Elsevier Ltd. All rights reserved. n Corresponding author. E-mail address: jamal.chaouki@polymtl.ca (J. Chaouki). Chemical Engineering Science 129 (2015) 193–207