Model based supervision of process engineering plants is difficult due to the complexities arising out of the energetic couplings in the model. In this series of two papers, it is shown how the Bond Graph as a multidisciplinary and integrated tool can be used for dynamic modeling and Fault Detection and Isolation heal of process engineering including (energetic and chemical phenomena). In this first paper a pseudo Bond Graph model technique is applied to a pilot plant reactor equipped with a mono-fluid heating/cooling system. A modeling structure has been implemented according to the process sub-units reactor, jacket, supply system and heating/cooling system and validated through experimental observations. In the sequel of this paper, the use of Bond Graph techniques is proposed to indicate the appearance of undesirable product in the reaction mixture, so as to elaborate an efficient and sensitive method for early warning detection of runway. In the second part, the causal and structural proprieties of obtained Bond Graph are used not only to validate the model, but also to provide the computational algorithms to eliminate unknown variables from coupled thermo-chemical models and thus generate Analytical Relations (ARRs) in terms of measurements and parameters for online diagnosis.