Removal of monomer from polymer

The reduction of monomers, usually referred to as VOCs, in various polymer suspensions is now a vitally important step in polymer production. VOCs must be reduced in order to meet increasingly stringent legislative requirements as well as specific customer needs and quality targets.

Due to the high viscosity and solids concentrations of many polymer suspensions (typically in the range 1000 to 5000 cP) conventional continuous stripping or distillation techniques, using packed or plate columns, are simply not viable. Polymer manufacturers are forced to adopt inefficient batch steam-stripping processes that can take hours to reduce the VOC concentrations to the required targets. 

FT Technologies is able to change this situation by processing high viscosity polymer suspensions continuously through its Spinning Cone Column (SCC). The FT Industrial SCC is a spinning cone liquid-gas contacting column, commonly used for steam stripping applications. Due to the SCC’s unique internal design, high mass transfer efficiency is combined with the ability to process viscous materials and liquids containing high levels of suspended solids. The system offers a number of advantages over traditional batch stripping methods including:

• Lower steam usage leading to reduced cost of production
• Short residence time that protects the average molecular weight
• Ability to handle rapid film forming polymers in an air free enviroment
• Compact, continuous, skid mounted system designed for CIP
• Modular design for future capacity increases
• Various levels of automation including completely automatic if required

One such polymer successfully processed is poly vinyl acetate (PVA) where the main VOC present is the monomer, vinyl acetate. After the polymerisation reaction is completed the polymer suspension typically contains vinyl acetate at a concentration in the range 500 to 2000ppm. Using the SCC vinyl acetate removal rates are typically in excess of 99.5%.

For applications where steam stripping is not possible, such as the removal of toluene diisocyanate (TDI) from a prepolymer, FT Technologies offers its short path distillation system based on the RM series Centritherm evaporator. This system uses spinning cones to create a thin turbulent film and offers a number of advantages over other short path systems including:

• Compact, continuous system requiring a low head height for installation
• Short residence time which helps to protect the average molecular weight
• Low hold up volume leading to minimal losses on start up and shutdown