An expert in the field of chemical engineering offers advice to resin manufacturers.

QUESTION: We produce many types of synthetic resins in our coating plants, and for each type we must comply with several formulations. Is there an easier, more reliable way to monitor product viscosity and determine the end of a reaction other than classical manual sampling and laboratory testing?

ANSWER: There are reactor-mounted viscometers with probes inserted in the reactor. Generally, they are unreliable because of inaccurate temperature measurements and interference with nitrogen bubbles or solid particles in the reactor contents.

The best and most accurate way to monitor viscosity is through online continuous viscosity measurement, where a small quantity of product is circulated through a viscometer mounted in an independently temperature-controlled enclosure near the reactor.

Such a system is used for alkyd, polyester, epoxy resins and polycondensation reactions. It presents several advantages, including the following.

• The signal generated by the viscometer is directly correlated to the product viscosity. It represents a real-time measurement and is a reliable way to monitor the reaction process.
• This viscosity monitoring can be made at temperatures different from the reactor temperature, thus allowing flexibility with instrument calibration and selection of the viscosity range.
• The end of the reaction can be exactly determined, thus eliminating off-spec product and waste.
• The process can be entirely automated, thus reducing batch time and operating costs.
• Product quality as endpoint viscosity can be achieved for each formulation.

Disadvantages to online continuous viscosity measurement are as follows.

• To operate the system, a flanged connection must be available or installed on the lower section of the reactor. This may not always be an option with existing equipment.
• The system is limited to resin manufacturing reactions where viscosity evolves during the batch and represents a valuable parameter to monitor.

Bernard Seguy is President of RHE America. He holds a Master's Degree in Chemical Engineering from the University of Lille in France.

For more information, contact RHE America, 2525 Cabot Drive, Suite 205, Lisle, IL 60532; phone (630) 577-0400; fax (630) 577-0401; e-mail info@rhe-america.com; or visit http://www.rhe-america.com.