Environmental and eco-costs life cycle assessment of an acrylonitrile process by capacity enlargement in Mexico

Life cycle assessment and marginal prevention costs (eco-costs method) for an acrylonitrile plant were carried out estimating the environmental impact and the eco-costs, due to the increment in the production capacity. This study compares the old plant's operative performance (old design) at 50,000 ton/year where the by-products were incinerated, with the current operation at 60,000 ton/year where those by-products in the waste stream will be treated to take advantage of its substance content, to generate profitable products. In addition, the effect of a wastewater flow rate with cyanide was evaluated on the biological wastewater treatment process.The redesign showed a high reduction percentage in eleven of eighteen midpoint impact categories. The reduction of 36% in the global impacts in the redesign was obtained when these ones were calculated based on the impacts of the year of 2005. The CO2 emissions equivalents (CO2eq) had a reduction of 46% (from 6.55 to 3.50 kg CO2eq/kg of acrylonitrile). The total of marginal prevention costs (eco-costs) are 1.28 USD/kg for acrylonitrile old design and the 0.735 USD/kg for acrylonitrile redesign, i.e. 42.5% lower than the old design. This means that 94.5% are costs for pollution and the use of energy and 5.4% by depletions of material resources.This study proved that the redesign is environmentally most favorable and economically affordable method.Eco-costs method should be incorporated as part of the financial indicators of a project, but with the respective adaptation to the environmental and economic conditions of a region.