Method and apparatus for polymer drying using inert gas

Abstract

Method and apparatus for drying granular resin material by heating compressed air to a temperature prescribed for gas separation membrane operation, presenting the heated compressed air to a membrane separating out oxygen-size and smaller molecules to provide a stream of gas molecules of at least nitrogen-size at a pressure substantially that of the compressed air, heating the stream of gas molecules of at least nitrogen-size to a temperature at which dew point of the stream is no higher than -40 degrees F., and introducing the heated stream of gas molecules into a chamber for upward flow to atmosphere through granular resin material in the chamber.

Description

CROSS REFERENCE TO RELATED PATENT APPLICATIONS[0001]This patent application claims the benefit of the priority of U.S. provisional patent application Ser. No. 62 / 652,612, filed 4 Apr. 2018. The priority of the '612 application is claimed under 35 USC 120.INCORPORATION BY REFERENCE[0002]This patent application incorporates by reference the disclosure of U.S. Pat. No. 6,584,701 issued 1 Jul. 2003.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT[0003]Not applicable—this invention was conceived and developed entirely using private source funding; this patent application is being filed and paid for entirely by private source funding.BACKGROUND OF THE INVENTION[0004]This invention relates to apparatus and methods for drying solid granular material. The invention is more particularly concerned with apparatus and methods for reducing the moisture content of solid particulate of pelletized material, specifically granular resin material, prior to molding or extrusion thereof.DE...

AI Technical Summary

Benefits of technology

This patent addresses the problem of degradation of polymers, such as nylon and polybutylene terephthalate, during the drying process. The invention provides a method and apparatus for drying these polymers in the absence of air or oxygen using nitrogen or other inert gases as the drying atmosphere. This results in higher drying temperatures, reducing the time the polymer is exposed to heat and minimizing degradation. The invention can be used with granular, regrind, and powdered polymers, and allows for one or more temperatures to be used. It provides faster drying times and maintains desirable properties of the polymer, such as strength, ductility, and color stability.

Problems solved by technology

Notwithstanding their wide use, desiccant type drying systems have significant drawbacks.

When used over a period of time, the desiccant material becomes loaded with water and loses its effectiveness as a drying media.

In granular resin drying systems using a single desiccant unit, down time associated with desiccant regeneration results in reduced granular resin material throughput.

Systems employing multiple desiccant units can avoid this problem, but they are more expensive due to the need to provide additional desiccant units and correspondingly more complex systems controls.

This is an ongoing problem in that nylon, polybutylene terephthalate, polylactic acid polymers, and thermoplastic polyurethane are some of the most widely used plastic polymer materials in the world.

Their property of degrading when exposed to oxygen at high temperatures, which high temperatures are normally necessary to dry these polymers so that they may be processed by molding or extrusion into finished articles, presents continuing problems for molders and extruders.

Use of lower temperatures slows the drying process, thereby requiring additional time for drying the polymer before the polymers can be processed into finished articles.

With the continuing need for efficiency in the plastics processing industry, the extended drying time at lower temperatures for these polymers is a continuing problem and issue for the processors.

The degradation in performance experienced by these polymers when heated to relatively high drying temperatures in the presence of oxygen include reduction in strength, loss of ductility, changes in color, changes in viscosity of the polymer when it is extruded or molded, changes in the chemical resistance of the polymer, reduced stiffness, and reduced stability of the polymer.

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