Polyurethane is one of the most versatile polymers. It appeared at the end of the 1930s and is used as an insulating, coating, adhesive and solid plastic material. Polyurethane can be produced in different forms: flexible and cross-linked foam, elastomer or coating. It is in high demand all over the world and particularly in China.
For online viscosity measurement in distillation and evaporation processes of MDI/TDI
Polyurethanes are produced by reacting an isocyanate, usually TDI (toluene diisocyanate) or MDI (methylene diphenyl diisocyanate) with a polyol (e.g. ethylene or propylene glycol). Depending on the expected end product, additives or other ingredients are incorporated to obtain the desired formulation.
During the manufacturing process, raw materials are pumped from their storage tank to a pressure reactor; where they are heated and stirred, monitoring pressure and temperature.
“Pure” MDI or TDI is produced by the reaction of a diamine (MDA or TDA) with phosgene. The crude diisocyanates are then fractionated in a distillation column to produce purer mixtures of isomers. At the bottom of the column, a mixture of MDI or TDI and tar is sent for recovery through an evaporation and drying process to increase the yield of the MDI/TDI unit.
Viscosity is a crucial parameter for the evaporation of MDI/TDI and can also be beneficial in other manufacturing cycles. Precise control of viscosity and temperature enables the evaporator residue content to be accurately monitored, which in turn provides reliable information on the proper functioning of the process.
The installation of a MIVI viscometer allows a viscosity measurement to be carried out directly on the reactor or on a pipe angle, at the outlet of the evaporator or the distillation tower. The MIVI viscometer allows monitoring of the residue to ensure that sufficient product has been recovered. It also makes it possible to control the final quality of the product.