Sustainable P2 design for batch-based specialty chemical manufacture

A case study has been conducted on the reduction of n-methyl-2-pyrrilodone (NMP) solvent waste in the manufacture of polyimide and polybenzoxazole precursors. The evaluation includes the environmental and economic assessment of solvent recovery and substitution strategies. A two-step distillation process proved effective in recovering 95% of the NMP at a purity of 99.97% from the aqueous solvent waste stream. Yearly operating costs were reduced by 83% and total life cycle emissions were reduced by 44%, due to reduction in virgin NMP use and hazardous waste disposal. With capital acquisition, the recovery option would still result in a net present value (NPV) at 10 years of $3,120,000. The reduction in life cycle emissions is limited by the thermodynamics of the system, in particular the large composition of water in the waste stream which requires significant energy to distill. Substitution of NMP with dimethyl sulfoxide (DMSO) and sulfolane reduces life cycle emissions by 44% and 47%, respectively, even without recovery, due to their greener manufacturing profile. Although, when the recovery system is integrated, no further reductions in the environmental impact are seen. This demonstrates the need for a complete analysis of a greener design, since the thermodynamic characteristics of the solvents are important to the life cycle assessment. Water reuse was also considered for the overall process, but is not recommended due to the high cost of treating the wastewater to ultrapure water standards