Life cycle assessment of solvent extraction as a low-energy alternative to distillation for recovery of N-methyl-2-pyrrolidone from process waste

Abstract

This case study investigates low-energy alternatives to distillation for the recovery of N-methyl-2-pyrrolidone (NMP) from solvent waste in the manufacture of resin precursors. Evaluation includes environmental and economic life cycle assessment of solvent recovery and reuse using batch distillation, solvent extraction, and solvent extraction at a sister plant. Solvent extraction at the sister plant involved shipment of hazardous waste to a facility with existing solvent recovery equipment and lower purity standards for NMP. The amount of processing required to recover useful NMP is reduced, increasing reductions in life cycle emissions and damages to the environment. Extraction at the sister plant recovered 98% of the NMP at a purity of 97.1 wt% from aqueous waste containing 17 wt% NMP. Extraction at the sister plant reduced total and CO2 life cycle emissions by 61% and 59%, respectively. Compared to the distillation recovery alternative, extraction at the sister plant results in reductions of 32% and 33% for total and CO2 life cycle emissions, respectively. Annual operating costs were reduced by 80%, with no capital investment, due to utilization of existing equipment. This resulted in a 10-year net present value (NPV) of $4.20 million, whereas distillation resulted in a 10-year NPV of $3.12 million.

Systematic Design of Solvent Recovery Pathways: Integrating Economics and Environmental Metrics

“…The complexity of the problem is compounded further due to numerous alternative process technologies that can be considered at each stage. These technologies include sedimentation, , filtration, , precipitation, , centrifugation, distillation, ,− pervaporation, ,, aqueous two-phase extraction, − and micro-, , ultra-, − and nanofiltrations. − The challenge, therefore, is to select appropriate technologies at each stage that can achieve the recovery and purity requirements and reduce capital, operating costs, and environmental impacts. A superstructure approach is a potential solution to this problem and has been used extensively in the process synthesis field. − Superstructures can capture all detailed structural possibilities by simultaneously comparing technology alternatives via the inclusion of mixers, splitters, bypasses, and connecting streams …”