A novel concept of a gas-liquid catalytic reactor, the so-called in-line-monolithic reactor (ILMR), is presented. According to this concept, the catalytic reactor is not separate vessel but, operating in a horizontal position, forms an integral part of the pipeline. Blocks of monolithic catalysts provide large numbers of parallel horizontal capillary channels, in which the reaction between the pre-dispersed gas and the liquid tal;es place. Based on the experimental kinetic data, a model of a commercial large-scale hydrogenation process in the ILMR has been developed. Comparative analysis of mass transfer conditions in the conventional reactor filled with particulate catalyst and in the monolithic unit shows very strong diffusional limitations in the catalyst particles and much higher catalytic effectiveness in the washcoated monoliths. Results of the reactor simulation indicate that the ILMR concept may lead to a very significant reduction of the equipment size for the process investigated.