Trickle-bed reactors (TBR) are often applied in chemical and petrochemical industry. The performance of these reactors can be improved substantially by periodic operation of the liquid feed and/or operation in the natural pulsing flow regime. The aim of this pilot plant study is to present a flow map for the cumene-hydrogen system at elevated pressures, and to evaluate the reactor performance improvement obtained by periodic operation of a trickle-bed reactor. The experiments presented in this work are performed in a pilot plant reactor of 0.051 m diameter and 1.2 m length. The transition from trickle to pulsing flow depends on fluid physical properties, operating conditions, and geometrical parameters. Although many industrial trickle-bed reactors using organic liquids are operated at high pressure, the transition map for these systems is scarcely reported in literature. In this study, the effect of operating pressure on transition from trickle to pulse flow has been investigated in the pressure range of 0.14-2.0 MPa. The boundary between trickle and pulse flow shifts towards higher superficial liquid velocity when the operating pressure increases. The hydrogenation of a-methyl styrene (AMS) over 2 wt.% Pd/C catalyst was selected as test reaction. The reaction is performed at a liquid inlet temperature of 40 degreesC and at an operating pressure of 0.2 MPa. The cyclic operation mode is compared with the trickle operation mode. It is found that periodic operation results in a significant improvement in reaction rate. (C) 2004 Elsevier B.V. All rights reserved.