Water recovery and recycle in the PVC production: A novel approach using membrane technology

The production of 1 ton of PVC requires 2.0 - 2.5 m3 of demineralised water. Some of the water is lost in the process, e.g. as vapor during the drying of the PVC or as sealing water, while approx. 80% of the water could potentially be recycled. In today’s installations only about 20 – 25% of the water recovered by the PVC decanter is used for flushing of the facilities, while 75 – 80% is discharged from the facilities after biological treamtent. The key challenges preventing the direct recycling of the water from the decanter to be used not only for flushing but also for the polymerisation is the presence of residual PVC particles and inhibitors. A new concept based on reverse osmosis does not only remove the residual PVC particles but also the inhibitors and conductivity down to levels allowing the direct recycle of 75 – 80 % of the water from the decanter to the polymerisation step. In this concept the water from the decanter is treated with special reverse osmosis membranes and modules. The result is a permeate stream suitable for direct recycling not only reducing the consumption of de-mineralised fresh water but also the amount of waste water to be treated. Applying a optimsed cleaning method membrane fluxes and thus the plant capacity can be maintained over long periods