Environmentally friendly processes are characterized by four indices: requirements of raw materials and energy, lost work due to non-equilibrium operations, and environmental load of by-products disposed. The relations between the indices and the structures of chemical reaction systems in the process are discussed. 1) Dehydrogenation of methanol to formaldehyde is endothermic, but the coupled reaction with oxidation of hydrogen is exothermic. The methanol/air ratio is adjusted so that the heat of reaction sustains the required reaction temperature. Thus, no heating or cooling is necessary and the lost work due to a heat transfer operation is ignored. 2) Acetic acid may be produced by the reaction of methane and carbon dioxide, which has a greenhouse effect. The reaction can be carried out in two stages: in the first stage, the carbon dioxide reforming of methane makes a mixture of carbon monoxide and hydrogen, from which acetic acid is produced in the second stage. 3) In the direct chlorination of methane to carbon tetrachloride, half of the chlorine fed is converted to hydrogen chloride, which is toxic to human health and the environment. Two chemical reaction networks which involve no problem of hydrogen chloride disposal are proposed.