Comparative environmental assessments of VOC recovery and recycle design alternatives for a gaseous waste stream

Decisions involving chemical process design, including selection of technologies and operating conditions, should integrate environmental considerations. The assessment methodology presented in this article includes nine environmental and human health impact indices, a "level I" multimedia fate and transport model, and an air emissions estimation calculator based on emission factors and correlations. The methodology and software tool was used to evaluate two case studies involving mixed-solvent recovery from a gaseous waste stream utilizing output from a commercial process simulator. The assessment methodology was applied for two evaluations: (a) separation technology selection and (b) choice of process operating conditions. It was found that two adsorption technologies with either steam stripping or vacuum regeneration are superior to three absorption technology configurations based on environmental and health indices. With suitable weightings, a single process composite index was defined and served as an environmental objective function for the evaluation of absorber oil flow rate changes using a single absorption technology configuration. It was found that the process composite index exhibited a reduction in environmental impact of 94% when operated at the "environmental impact minimum" absorber oil flow rate, compared to releasing the VOCs directly to the environment.