Estimating the Environmental Impact of Catastrophic Chemical Releases to the Atmosphere: An Index Method for Ranking Alternative Chemical Process Routes

Abstract

This paper presents an index called the atmospheric hazard index (AHI), which can be used to assess the potential impact of airborne releases from a chemical production plant. A catastrophic failure of the plant is assumed and the impacts on the atmospheric environment are estimated. The method is designed for assessing possible alternative process routes [the raw material(s) and the sequence of reaction steps that converts them to the desired product(s)] to make a chemical, in order to determine the route that has the least adverse atmospheric environmental impact. Thus the routes that are inherently environmentally hazardous can be identified and avoided when the selection is made in the early stages of production plant design. The atmospheric impact categories considered are toxicity, photochemical smog, acid deposition, global warming and stratospheric ozone depletion. The magnitude of these impacts are expressed on a scale of 0 (minimum) to 10 (maximum). Each of these impact categories is assigned an importance factor value (I) depending upon: the spatial scale affected by, the degree of ‘directness’ of and the reversibility of the impact. These factors are used to calculate a weighted category hazard (WCH) value for each chemical. The WCH of all the impact categories and chemicals are combined to estimate the AHI. The AHI has been tested on six potential and established routes to methyl methacrylate (MMA). The route based on propylene has the lowest AHI value. In all the routes the storage inventory has the potential to cause the most environmental damage compared with the reaction and separation inventories.