What Is the Role of PTFE Exchangers in Bromine Recovery from Seawater and Brines?

Bromine is a thick, caustic liquid and vapour used in flame retardants, water treatment and pharmaceuticals. It is recovered from seawater and brine wells by oxidation with chlorine and then steam stripping. The heat exchangers in this process will have to be resistant to moist bromine, chlorine and hot brine -- a combination few materials can survive.

Recovery Process of Bromine
The recovery of bromine from saltwater and brines comprises several essential phases. The bromine ions in the brine are oxidised by chlorine gas, which changes them into elemental bromine. The steam is then used to remove this bromine from the brine. The vapour combination, which consists of bromine and water, is chilled in condensers. The cooled vapour is separated into liquid bromine, which is collected for further use.

The recovery process uses high temperatures and harsh chemicals. This makes the choice of materials for heat exchangers particularly important.

Bromine Recovery Material Problem
In addition to its liquid form, wet bromine in either phase (liquid or vapour) is quite corrosive to many materials. When mixed with chlorine, the chemicals become more aggressive. Corrosion is especially problematic for metals such as stainless steel, titanium and copper when exposed to bromine and chlorine. Heat exchangers used in the recovery of bromine must therefore be made of materials that can resist bromine and chlorine without deterioration.

One of the few polymers that can tolerate the corrosive action of moist bromine and chlorine at moderate temperatures, typically below 100 °C, is polytetrafluoroethylene (PTFE). Its superior chemical inertness makes it suitable for use in applications where there is both bromine and chlorine, ensuring reliable performance in severe settings.

Application of PTFE Heat Exchanger
In the bromine recovery process, PTFE heat exchangers are employed in a number of steps within the process. These exchangers find utility in applications such as:

Brine Pre-heaters: PTFE heat exchangers can be used for pre-heating the incoming brine, which is critical for successful bromine extraction. These exchangers are used to recover heat from the outgoing brine or other process streams to optimise energy utilisation.

Condensers for Bromine Vapour. After stripping the bromine from the brine using steam, the bromine-water vapour mixture is condensed in order to recover the liquid bromine. PTFE exchangers for condensers keep the bromine cool, even when exposed to bromine and chlorine vapours, without degrading the material.

Product Bromine Coolers The recovered liquid bromine must be cooled prior to storage or further processing. PTFE exchangers deliver the necessary cooling, without the risk of corrosion or contamination.

PTFE heat exchangers are needed for reliable and long term operation in these harsh settings due to their resistance to bromine and chlorine.

Technical Stuff
Bromine Recovery Temperatures: Temperatures in bromine recovery are normally in the range of 80-100°C. PTFE is well suited to manage these temperatures with a maximum continuous operating temperature of about 110°C.

Material Compatibility PTFE is resistant to the presence of bromine and chlorine in the liquid and vapour phases up to the temperature limit of the PTFE. More severe conditions can be applied with PFA (perfluoroalkoxy) or PVDF (polyvinylidene fluoride) due to their better temperature resistance and improved mechanical qualities.

Material Compatibility Note Material Max. TemperatureCorrosion Resistance to Bromine Suitability for Bromine Recovery Resistance to Chlorine PTFE 110°C Excellent Excellent Ideal for moderate temperatures and aggressive bromine-chlorine combinations
PFA ~260°C Excellent Excellent Better mechanical qualities for high temperature applications
PVDF ~150°CGood Good Good for less aggressive bromine service at moderate temps.
Tantalum ˜300°C Very Good Very GoodGreat for hot heat but quite pricey.
As indicated, PTFE, PFA and tantalum are the most suitable for bromine recovery service. PTFE is the most widely used because it is inexpensive and performs well at moderate temperatures.

Summary
PTFE heat exchangers are key to the recovery of bromine from saltwater and brines, and show excellent resilience to the hostile mix of wet bromine, chlorine and high temperatures. These exchangers are critical to the effectiveness of the recovery process, reducing downtime caused by corrosion and protecting the purity of recovered bromine. With ever increasing demands on material performance for halogen processing, PTFE exchangers remain a trusted choice for the difficult conditions of bromine recovery operations.

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