Life-cycle assessment of chemical production processes: A tool for ecological optimization

Life-cycle assessment (LCA) has gained in recent years widespread acceptance as an environmental management tool to assess and valuate the environmental impacts (resource consumption and emissions to nature) of products and processes, covering the whole life cycle from cradle (extraction of raw material) to grave (final disposal). Applied to chemical manufacturing, LCA allows to compare the ecological performance of synthesis processes, guide process developers to weak points and improvement options, and avoid suboptimizations. Ln our Consumer Care Chemicals Division, we apply LCA routinely to sales products as well as manufacturing-process chains, and we developed a specialized LCA computer system ECOSYS for that purpose. Material flow, energy, and waste data for all in-house manufacturing processes are extracted from our company data bases into ECOSYS. For meaningful comparisons of whole life cycles, we must include LCA results for the raw materials bought from other suppliers, and since such data are rarely available, appropriate estimation procedures were developed. The multitude of ecological burdens calculated over the life cycle can be judged and compared by a variety of valuation schemes, e.g. according to the Swiss BUWAL or the modern Eco-indicator 95 method. ECOSYS is not restricted to existing, operational processes, but allows the process developer to-test his hypothetical designs (e.g. derived from a simulation tool) at a very early stage. If process alternatives use different raw materials, a narrow judgement on data for the process step alone may lead to suboptimization, whereas LCA results that consider all preceding syntheses of intermediates allow a more objective comparison. As an example, two synthesis paths for DNS (4,4'-dinitro-2,2'-stilbenedisulfonic acid disodium salt) were compared: The older, established route uses NaOCl in aqueous media as an oxidant, whereas the method more recently introduced in one of our production plants is based on air oxidation in liquid ammonia. The latter produces considerably less waste and is favorable with respect to many ecological parameters, including energy consumption, over the whole life cycle.