Schkopau , Germany – The Fraunhofer Institute and Swiss company List AG has developed a low-pressure steam technique, which is claimed to reduce solvent-removal costs in the manufacture of synthetic rubber by around 50 percent.
The manufacture of synthetic rubber via solution polymerisation usually requires the use of large amounts of energy to separate solvent from the end polymer.
The solvent-removal process is particularly difficult because the rubber tends to crosslink when exposed to heat and mechanical stress.
The Fraunhofer Pilot Plant Center for Polymer Synthesis and Processing PAZ in Schkopau joined forces with the List AG to find new ways to protect the rubber polymer when it is separated from its solvent.
The project saw the installation of two knead reactors at the Fraunhofer PAZ, a joint facility of the Fraunhofer Institute for Applied Polymer Research IAP in Potsdam-Golm, and the Fraunhofer Institute for Microstructure of Materials and Systems IMWS in Halle.
Using a process developed with List AG, the research team used direct evaporation to achieve a 75-percent saving in energy usage.
The knead reactors were used in combination with a special concentration technology for temperature-sensitive polymer solutions.
During conventional coagulation, heat measuring around 100°C is applied for several hours. In a process developed in 2007, rubber polymers are isolated in a knead reactor which requires temperatures of between 70-90°C and a dwell time of 30 minutes.
The use of this technology has very little impact on the material properties, while the solvent that accrues is almost exclusively water-free. The laborious process of drying the solvent can, therefore, be greatly optimised, which saves additional costs.
The project team, therefore, subsequently introduced an additional process step that allowed the use of inexpensive, low=pressure steam. This delivered energy cost savings of more than 50 percent regardless of the material and the viscosity of the rubber solution used.
“The process we have developed has enabled us to make considerable advances in isolating rubber polymers. We have improved our understanding of the process over the years,” said Dr. Ulrich Wendler, who heads up synthesis and product development at the Fraunhofer PAZ.
According to Wendler, the basis for this optimisation is the ability to scale up information from the pilot plant scale to a scale that is relevant for industry. Process data is collected for both the lab scale (kneader with 2.5 and 4 litre volumes) and the pilot plant scale (100 and 200 litres).
“It isn’t until there is a scaling up by more than two orders of magnitude that the true process and material challenges are revealed,” he explains.
(Lead Photo © Fraunhofer IAP, photographer: Alexander Krause)