Moisture of synthetic rubber

A major producer of synthetic rubber has selected Michell Instruments’ Liquidew I.S. moisture in liquids analyser to monitor critical process at its plant in Asia.

The plant produces Polybutadiene, a form of synthetic rubber, commonly used in the manufacture of car tyres. This is generated from a feedstock of the gas 1,3 Butadiene, which is pressurised to form liquid phase and then dissolved in Hexane. The reaction to form the Polybutadiene requires a catalyst, which in this case is an alkyl-lithium compound. Lithium is highly reactive with water and will only be an effective catalyst in near-anhydrous conditions where there is no more than 1ppmW of moisture present.

In total, six Liquidew I.S. analysers are installed at key points in the process to monitor moisture levels in the feedstock and the solvent as well as in the drying process used to regenerate the solvent. The Liquidew I.S. is capable of measuring moisture levels down to 0.001ppmW and can reliably give accurate readings in the low-moisture environment.

After the reaction has taken place, the Hexane solvent is evaporated to separate it from the newly-produced Polybutadiene using hot water in a separate vessel. It is then dried and purified before being re-introduced into the process.

Because water is used to clean and recycle the hexane solvent, there is a risk of moisture contaminating the process if the solvent is not dried sufficiently before being reused. The solvent is dried in molecular sieve towers and this drying process is repeated many times until the purity and dryness is sufficient for reintroduction into the process.

The Liquidew I.S. was selected for this application because it measures from 0.001 to 1000 ppmW with a fast response and recovery time, allowing it to rapidly indicate changes in moisture concentration. This is ideal for the drying process as it can reduce the number of drying cycles required to dry the solvent.

• Michell Instruments are marketed in Ireland by Instrument Technology.