The influence of baffle clearance design on the liquid circulating velocity, gas holdup and pressure drop in a two riser rectangular airlift reactor with inverse internal loop and expanded gas-liquid separator was investigated using water and mineralized CMC solutions covering a range of effective viscosity from 0.02 to 0.5 Pa s and surface tension from 0.065 to 0.085 N/m. The gas holdup results in the riser, downcomer, and gas-liquid separator were satisfactorily derived using expressions obtained via dimensional analysis. The separator gas holdup was found to be similar to the total gas holdup in the airlift reactor. The baffle clearances were found to influence the liquid circulation velocity to some degree, with the bottom clearance being the significant design parameter. An attempt was also made to correlate the liquid velocity using empirical equations of the loss coefficient in the baffle top and bottom zones. The calculated and observed liquid circulation velocity agreed well with an error of +/- 29% for the air-water system. (c) 2006 Elsevier B.V. All rights reserved.