Chemical Engineering Journal 128 (2007) 69–84 Gas holdup and bubble size behavior in a large-scale slurry bubble column reactor operating with an organic liquid under elevated pressures and temperatures Arsam Behkish a , Romain Lemoine a , Laurent Sehabiague a , Rachid Oukaci b , Badie I. Morsi a,∗ a Chemical and Petroleum Engineering Department, University of Pittsburgh, Pittsburgh, PA 15261, USA b Energy Technology Partners, 135 William Pitt Way, Pittsburgh, PA 15238, USA Received 14 October 2005; received in revised form 4 October 2006; accepted 6 October 2006 Abstract The holdups of small and large gas bubbles, bubble size distribution and the Sauter-mean bubble diameter were measured for N 2 and He in isoparaffinic organic liquid mixture (Isopar-M) in the absence and presence of Alumina powder under various pressures (0.67–3 MPa), temperatures (300–473 K), superficial gas velocities (0.07–0.39 m/s), and solid concentrations (0–20 vol.%) in a large-scale bubble column and slurry bubble column reactor (SBCR) (0.29 m diameter, 3 m height). The gas holdup was measured using the manometric method and the bubble size distribution, and Sauter-mean bubble diameter were obtained using the dynamic gas disengagement (DGD) technique and the photographic method. The experimental data showed that the total gas holdup increased with pressure and superficial gas velocity due to the increase of gas momentum which shifted the bubble size distribution towards smaller gas bubbles. The total gas holdup was also found to increase with temperature due to the decrease of liquid viscosity and surface tension. Increasing the solid concentration, on the other hand, resulted in a significant decrease of the total gas holdup and significantly increased the Sauter-mean bubble diameter. The online monitoring of the swarm using the high-speed camera showed a decrease of the froth stability in the reactor with increasing solid concentration and temperature which were responsible for the decrease of the total gas holdup. © 2006 Elsevier B.V. All rights reserved. Keywords: Slurry bubble column reactor; Gas holdup; Bubble size distribution; Sauter-mean bubble diameter; Dynamic gas disengagement; Fischer–Tropsch synthesis 1. Introduction Commercial processes conducted in slurry bubble column reactors (SBCRs), including Fischer–Tropsch and methanol syntheses, are generally carried out under high pressures (1–8 MPa) [1], temperatures (500–541 K) [1–4], and gas super- ficial velocities (0.095–0.35 m/s) [2,3], with (30–40 vol.%) cata- lyst loadings [1,4], in large-diameter (5–8 m) reactors [1]. Under such wide ranges of operating conditions, the physicochemi- cal properties of the three-phase system are greatly affected, influencing the kinetics, hydrodynamics, and heat/mass trans- fer characteristics, and subsequently the selectivity and yield of the process. For instance, under high pressures, temperatures, ∗ Corresponding author. Tel.: +1 412 624 9650; fax: +1 412 624 9639. E-mail address: Morsi@engr.pitt.edu (B.I. Morsi). gas superficial velocity and catalyst loading, the slurry as well as liquid-phase viscosity, density, surface tension, and foaming tendency are altered, affecting the formation and stability of the gas bubbles and consequently the hydrodynamic and mass transfer behavior in the reactor. In SBCRs operating in the churn- turbulent flow regime, the mass transfer behavior is controlled by the gas–liquid interfacial area [5] and hence the knowledge of the gas holdup and bubbles size/distribution as well as the influence of operating variables on these parameters is essential for proper design and scale-up of such reactors. Table 1 summarizes available literature studies on high pres- sure, high temperature bubble columns and slurry bubble column reactors and the following observations can be made. Deckwer et al. [6] studied the hydrodynamic of Fischer–Tropsch in slurry process at elevated pressures (0.4–1.1 MPa) and temperatures (416–543 K) in two small-diameter SBCRs (0.041 and 0.10 m) operating in the homogeneous flow regime at superficial gas 1385-8947/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2006.10.016