Green Processing and Synthesis

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.

Crude dimer acid (DA) was prepared with soybean oil (SO) used as raw material and organic montmorillonite as a catalyst. Fourier transform infrared (FTIR) spectroscopy, hydrogen nuclear magnetic resonance (¹H-NMR) and gel permeation chromatography (GPC) were used to characterize the structure of DA. It was demonstrated that the synthesis of crude DA using SO was feasible. A molecular weight of 995–1304 g/mol was obtained by GPC measurement. Then, a type of polyester was synthesized using the crude DA and polyethylene glycol. The effects of reaction temperatures and different catalysts on the conversion rate were explored. The results showed that the esterification conversion rate was improved to 83.13% when SnCl₂ was used as the catalyst, with a reaction temperature of 180°C The FTIR, ¹H-NMR, GPC and TGA were used to characterize the structure and performance of this polyester. The polyester had a molecular weight ranging from 8259 to 10892 g/mol. In addition, its biodegradable behavior was analyzed by the soil burial test and was compared with that of terephthalic acid. The results showed that the composites prepared from DA had a pronounced effect on weight loss during biodegradation.

Green, sensitive and selective spectrophotometric methods were developed for the determination of nitrite in water samples. The methods (A, B and C) are based on the reduction of 5-nitroimidazoles; metronidazole (MTL), secnidazole (SCL) and tinidazole (TNL), respectively, followed by diazotization using nitrite in acidic medium, then coupling with pyrogallol (PG). The amount of nitrite was determined by measuring the absorbance of the colored product at 385 nm. The new methods were linear in the ranges of 2.5–30 μgml⁻¹, with detection limits of 1.4 μgml⁻¹.