The earlier approach to implementing the proxy data for heat demands frequently assumed, in cases of exothermal chemical reactions, that the generated heat from the chemical reaction would exactly match the heat demand for any subsequent purification steps and could therefore be neglected (e.g. nitrobenzene production) . Analyzing the literature data, however, shows that the mean energy release by exothermal reactions is around 2.7 MJ kg -1 , while the mean purification energy demand is at about 3.9 MJ kg -1 (17). In addition, the costs for heat recovery from exothermal reactions may in some cases be uneconomically high, resulting in non-implementation or limited use of heat recovery. Hence, neglecting any heat demands for exothermal reactions is in many cases an oversimplification that leads to an unnecessary underestimation of environmental impacts from chemicals production.