Ethanolamines are important basic chemicals, and a heat resistant catalyst having high selectivity and activity has been required for producing monoethanolamine and diethanolamine in larger amounts to satisfy the increasing demands. Nippon Shokubai developed a modified clay catalyst for selective monoethanolamine production. The heat capacity of a multicomponent system (ammonia, ethylene oxide, and ethanolamines) was measured with pilot equipment, and an experimental equation of heat capacity was presented. Because the developed catalyst has higher selectivity than that of ion exchange resins, operation with high concentration of ethylene oxide becomes possible. However, the large reaction heat of operation in an adiabatic reactor causes a severe temperature rise, which can affect product quality. Elimination of reaction heat is necessary to reduce the temperature rise, and utilization of the latent heat of ammonia vaporization is proposed as a solution. A selective monoethanolamine production process with high productivity has been developed by adopting a model of partial vaporization of ammonia and using the modified clay catalyst. (C) 2009 Elsevier B.V. All rights reserved.