Handbook of Solvents - George Wypych - ChemTech - Ventech!

14.22 Polymers and man-made fibers 1017
Figure 14.22.1. Schematic diagram of emissions from the polymer manufacturing industry. [Reproduced from
EPA Office of Compliance Sector Notebook Project. Profile of the Petroleum Refining Industry. US
Environmental Protection Agency, 1995.]
vent), and residual water and solvent are purged during polymer drying. Residual solvents
are removed by further drying and extrusion. Solvents are also used in equipment cleaning.
Solvents are often stored under a nitrogen blanket to minimize oxidation and contamination.
When these systems are vented solvent losses occur. Figure 14.22.1 shows a schematic
diagram of potential emissions during polymer manufacture.
Manufacture of man-made fibers involves polymerization (usually the core part of the
process), preparation of the solution, spinning, washing and coagulation, drying and other
operations. Fibers are formed by forcing the viscous liquid through small-bore orifices. A
suitable viscosity can be achieved either by heating or dissolution. The rheological properties
of the solution are governed to a large degree by the solvents selected. Wastes generated
during the spinning operation include evaporated solvent and wastewater contaminated by
solvent. The typical solvents used in the production of fibers are dimethylacetamide
(acrylic), acetone or chlorinated hydrocarbon (cellulose acetate), and carbon disulfide
(rayon). In the dry spinning process a solution of polymer is first prepared. The solution is
then heated above the boiling temperature of the solvent and the solution is extruded
through spinneret. The solvent evaporates into the gas stream. With wet spinning the fiber is
directly extruded into a coagulation bath where solvent diffuses into the bath liquid and the
coagulant diffuses into the fiber. The fiber is washed free of solvent by passing it through an
additional bath. Each process step generates emissions or wastewater. Solvents used in production
are normally recovered by distillation. Figure 14.22.2 is a schematic diagram of fiber
production showing that almost all stages of production generate emissions.