Dosing of corrosive monomers in a pressure reactor

Both batchwise and continuous dosing for an extremely accurate polymerization process

Until then, a supplier of biodegradable polymers used the classic production method. A reactor was filled with monomers and catalysts/auxiliary materials. The reactor was then stirred to effect a polymerization reaction. To optimize and/or modify this process, a solution was sought to allow monomers to be dosed into the reactor in a controlled manner, both batchwise and continuously.

Issue

The monomers that must be dosed into the reactor have a high melting point and must be processed at 150°C – 200°C. Moreover, the viscosity varies from 1 to 1,000 mPa·s and both the monomers and the added solvents are chemically aggressive. The materials used must therefore be corrosion resistant. The stirred vessel must be able to be under pressure (max. 5 barg) to inert. The available space in the fume cupboard is limited to 450 x 600 x 1000 cm.

Requirements regarding the system designed by Suurmond:

• A stirred vessel of ~2 liters that must be able to stand under nitrogen (up to 5 barg) and vacuum to inert
• Temperature range: >150°C (max. 200°C)
• Viscosity 1-1'000 mPa·s
• Being able to accurately regulate volume flow from 1-100ml/min.
• Gravimetric/volumetric checking/regulation of the volume flow
• Tracing of the entire system to prevent solidification of the substances
• Corrosion resistant materials
• Maximum back pressure in reactor vessel is 5 barg
• Available, limited space in fume cupboard (WxDxH) 450 x 600 x 1000 cm
   

Our solution

Suurmond designed a compact dosing system with a heatable pressure vessel on a small platform that had to be mounted next to the existing reactor in the fume hood.

Pressure vessel

The system consists of a heatable stainless steel pressure vessel of our own design with a Büchi magnetic stirrer type “BMD 075” to keep the monomers moving and homogeneous. This stable magnetic stirrer is equipped with ceramic ball bearings and a Kalrez O-ring for corrosion resistance. The stirrer shaft and stirrer are also suitable for corrosive liquids, so that use with chemically aggressive liquids, such as solvents, is not a problem.
The pressure vessel is equipped with tracing to keep the monomers in the vessel liquid. The complete system is insulated with custom-made thermal insulation (mattresses).

Dosage

An HNPM micro gear pump type mzr-7255 was used to dose the monomers. To this end, it is equipped with an insulation module between the pump head and servo motor. This pump is therefore suitable for liquid temperatures up to 200°C (normally the pump is suitable for up to 60°C)! This micro pump can handle the wide viscosity range well. Moreover, due to the use of this gear pump, no pre-pressure is required.
With the mass flow meter, the flow can be easily measured and controlled in closed-loop. Both volumetric and gravimetric.

Controls

The controls are also custom-made. It is designed in such a way that you can set the dosage yourself and enter the process steps.

Result

With this setup the customer can dose the monomers into the reactor both batchwise and continuously. The suurDOS® ensures an optimized and extremely accurate polymerization process.