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Solvent Removal of Latex Using Hot Gas Injection

IP.com Disclosure Number: IPCOM000237510D
Publication Date: 2014-Jun-19
Document File: 4 page(s) / 44K

Publishing Venue

The IP.com Prior Art Database

Abstract

This idea discloses a new solvent removal method by injecting hot gas into a latex material to reduce the level of volatile organic compounds (VOCs). It allows for the removal of solvents in the latex without lowering solid content. The injected hot nitrogen bubbles transfer energy to the batch to vaporize solvents and take them out of the latex. This method is applicable to solvent removal of any latexes that can or cannot be distilled under high vacuum but require high solid content. This method is applicable to solvent removal for all solvent-based latexes and provides an alternative for solvent removal that can be quickly implemented with minimal equipment modification.

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Solvent Removal of Latex Using Hot Gas Injection

This idea discloses a new solvent removal method by injecting hot gas into a latex material to reduce the level of volatile organic compounds (VOCs). It allows for the removal of solvents in the latex without lowering solid content. The injected hot nitrogen bubbles transfer energy to the batch to vaporize solvents and take them out of the latex. This method is applicable to solvent removal of any latexes that can or cannot be distilled under high vacuum but require high solid content. This method is applicable to solvent removal for all solvent-based latexes and provides an alternative for solvent removal that can be quickly implemented with minimal equipment modification.

This idea is applicable to the production of latexes of crystalline and amorphous polyester resins (CPE, FXC42, and FXC56, corresponding to EP32, EP33, and EP34 latexes).  The proposal improves the conversion cost of resins to latexes and the distillation of latexes to remove solvents. The improvements of the phase inversion emulsification (PIE) and solvent stripping process for latex production, such as reduction of cycle times and processing costs, will help reduce the latex manufacturing cost.

Latex emulsions of polyester resins are currently produced using the PIE process in which the resins are dissolved in dual solvents (Methyl Ethyl Ketone – MEK and Isopropyl Alcohol – IPA), neutralized with an appropriate base, and mixed with water to create a homogeneous water-in-oil (W/O) dispersion (water droplets dispersed in continuous oil). Subsequently, additional water is added to invert this dispersion into self-stabilized oil-in-water (O/W) latex. Energy intensive processing of the latex is then used to remove virtually all traces of the organic solvents, and finally surfactant and other preservatives may be added to provide a stable latex with relatively high solid content of polyester. 

Currently, high vacuum is used to distill solvents for all three latexes. Since foam generation is a significant issue for fast distillation, the operators need extensive experience to adjust the vacuum level in order to remove solvents efficiently but also have foam generation to control. During the distillation process, the operators need to pull samples periodically and track the volatile organic compounds (VOCs) level via GC until it reaches environmental specification (300 ppm for MEK and IPA). Since polyester latexes are shear-sensitive and could form gelation at high solid contents due to un-even distribution of water among particles, operators also want to measure the solid contents and feed distilled water to latex to maintain it within a certain range. Because the vacuum pump applies high vacuum on latex and removes solvents very quickly, any minor mistake of operation during distillation could over-distill latex, resulting in latex gelation and failure of production. Therefore, the operator’s experience and attention are...