Production of 99.9% bromine from brines, debromination of brines down to 10ppm bromine
Use of Bromine
Bromine is widely used in the chemical and pharmaceutical industries. Major applications are brominated organic components used as
- Flame retardants (e.g. polybrominated biphenyls)
- Pesticide (e.g. methyl bromide)
- Reactive intermediates in organic synthesis and pharmaceutical ingredients
Sources of Bromine
Natural sources for bromine are chloride sources such as natural salt stocks and seawater where bromides are accompanying the chlorides. Industrial sources for bromine recovery are quench waters of waste incinerators (coming from the flame retardants) and effluents of industrial bromination processes.
The reactions to form the a.m. chemicals may generate hydrogen bromide as a by-product:
R-H+Br2 => R-Br+HBr
In this case no more than half of the bromine added ends up in the product, the rest being released as hydrogen bromide gas and as dissolved bromides (often rejected in washing solutions). Since bromine is an expensive, widely used raw material, recovery is usually a viable option.
Bromine is highly corrosive, toxic, and causes serious chemical burns. 3 ppm in the air are considered immediately dangerous to life and health. Therefore, it is vitally important to take the highest safety precautions when working with bromine.
Accordingly, plants processing bromine have to be made of highly corrosion and diffusion resistant, robust materials. QVF borosilicate glass 3.3 and De Dietrich glass-lined steel are ideal materials for their construction. All measures are taken to avoid any bromine leakage; the equipment fulfills ASME requirements for pressure and tightness of flange connections. For extra safety measures, the vent systems are equipped with bromine scrubbers.
De Dietrich Process Systems' material quality, detailed design and reliable process engineering contribute to the safe handling of bromine.
Treating Bromide Containing Brines
There are two different objectives when treating bromide containing brines. One objective is the production of bromine and the other one is to debrominate the brine to get rid of the bromides. The production of bromine from brines as well as the debromination of brines is based on the oxidation of bromide to bromine. In the laboratory scale an oxidating component (concentrated sulfuric acid or acidified KMnO4) is used. In the industrial scale mainly chlorine, but also hydrogen peroxide is used.
Production of Bromine
The production of bromine from brines becomes economically advantageous when the bromide concentration is more than 2.5 g/l. If seawater is used, it will have to be pre-concentrated, mostly by solar evaporation ponds, to reach that concentration. The production of bromine is done in two steps. In the first step the bromides are oxidized with chlorine and the bromine is stripped with steam in the same column:
2Br- + Cl2 => 2Cl- + Br2
The second step is the purification of the bromine from water and chlorine by rectification in a distillation column. These steps are carried out in columns interlinked as shown in block scheme A. The purification is eased by the fact that bromine has a low solubility in water (only 28g-Br2/1000g-H2O) so that efficient phase separators can be used. Purification is achieved by separating the chlorine and water from the bromine with a rectification column. Pure bromine (99.9%) can be withdrawn at the bottom of the thermal separation column.
Block scheme A - Bromine production
Bromide impurities in chloride brines can reduce the quality of the products made from chloride solutions, and can also hamper the process handling the chlorides. The QVF debromination process can reduce the bromide content in brines down to 10 ppm. The process shown in block scheme B is also based on the selective oxidation of bromides, which can be done either with chlorine or with hydrogen peroxide. Stripping of the bromine is done with recycled air instead of steam, and is also called “cold debromination”. If elementary hazardous bromine is not desired, it is reduced by sodium sulfite back to harmless bromide in a second absorption column:
Br2 + Na2SO3 + H2O => 2HBr + Na2SO4
Block scheme B - Debromination
Bromine Process Expertise
In order to make these plants most efficient, the columns and their internals have to be highly corrosion resistant and specifically constructed for the process. Their task is to equally distribute large feed streams and to redistribute them along the column to avoid dead volumes and to maximize the mass transfer area. This can be accomplished with our patented QVF CORE-Trays which ensure a maximum contact of the liquid phase with the gas phase generated by our structured packing (DURAPACK) made of borosilicate glass 3.3. The bromine is also safely handled by our corrosion resistant QVF shell and tube heat exchangers with tubes either made of borosilicate glass 3.3. or SiC. The proven bromine evaporators are made of tantalum.
While the above described processes are extremely comprehensive, the solution is not always simple since feeds are often contaminated with organic materials from the reactors. They have to be removed by steam stripping before entering the stripping column since they may react with bromine and consequently reduce the yield. Even in such difficult cases, our wide experience coupled with our extensive pilot plant facilities in Germany, allow us to find the right solution for removing organics and increasing the yield to provide you with the ultimate process design for your plant.