Separation and Recovery of Nylon from Carpet Waste Using a Supercritical Fluid Antisolvent Technique

Abstract

This article presents a new process for the selective separation and recovery of nylon material from carpet waste using a solvent-based selective dissolution technique combined with supercritical fluid antisolvent precipitation. The process is described in three primary stages: (1) selective dissolution of nylon up to 2.31 wt.% from the model carpet with an 88 wt.% liquid formic acid solution is performed at 40°C, (2) recovery of the nylon product powder with supercritical C02 antisolvent precipitation at pressures between 84 and 125 bar at 40°C, and (3) recycle of both the solvent and antisolvent by flashing into two phases. Detailed studies on the supercritical fluid antisolvent precipitation (stage 2) of the nylon material from carpet waste were performed in which the influences of operating conditions were examined. Effective recovery of the nylon material was achieved with control over the morphology and particle size of the nylon powder. The particles obtained were typically less than 20 μm and spherical in nature, with exceptions observed at the highest operating pressure above 300 bar. In general, the experiments illustrate that changes in operating pressures (both upstream and down-stream of the expansion nozzle), nozzle diameter, and solution concentrations had little influence on the particles' mean size and size distribution. The results suggest this process to be very controllable. In addition, analysis of the nylon product illustrated that this process shows promise in providing quality nylon material from waste carpet material.