The present invention relates to processes and systems for drying wet bromine liquid, and more particularly, in one or more embodiments, to processes and systems for drying wet bromine liquid in a system having two fractionators, one for separating substantially dry bromine from wet bromine liquid and another for separating substantially pure water from water having bromine dissolved therein.
Bromine has a wide variety of industrial uses, including in the preparation of disinfectants, chemical flame retardants, and photographic materials, in water purification processes, and as an intermediate in the manufacture of dyestuffs, drugs, resins and refrigerants. Bromine may also be used in the bromination of alkanes to produce alkyl bromides that in turn have uses in processes, such as the production of higher molecular weight hydrocarbons useful as chemical intermediates and as blending stock or fuels. Many of the uses prefer dry bromine containing less than 5 wppm water.
Wet bromine is highly corrosive and requires that components used to handle wet bromine be constructed of corrosion-resistant materials or coatings, such as tantalum, which are extremely expensive. As dry bromine is much less corrosive than wet bromine, it usually is advantageous to use dry bromine in most industrial processes employing bromine.
Some processes that have been proposed for drying bromine utilize a drying agent for the adsorption of water therefrom. However, the use of a drying agent is accompanied by many drawbacks. If the drying agent is a solid, for example an inorganic salt, solid incrustations form on the surface of the drying agent rendering the surface impermeable and therefore decreasing the efficiency of the drying agent. When liquid drying agents are used, for instance sulfuric acid, bromine may become contaminated with components of the drying agents. Another drawback in using drying agents is that the drying agent must be regenerated or additional fresh drying agent must be added or used at varying intervals.
In accordance with another process, liquid bromine having a water and chlorine content is kept at about its boiling point, gradually loses water and chlorine and over a period of time to drop the water and chlorine content to lower levels. While this process produces bromine with reduced water and chlorine content, it is not deemed commercially practical as keeping the bromine liquid at the boiling point causes significant loss of bromine with the evaporated water and chlorine. In addition, for large flow rates of bromine, the long residence time needed for this process requires large bromine storages which present tremendous hazard risk. Furthermore, this process does not achieve requisite low levels of water and chlorine.
Liquid crude bromine containing impurities, such as water and chlorine, is vaporized and heated to greater than 700° F. in accordance with another process, added to steam and condensed to form water and liquid bromine. The liquid bromine is separated from water and dried over concentrated sulfuric acid. The dried bromine is then distilled to remove its heavy end contaminants. The purified bromine produced having an overall purity of 99.98 percent or better, i.e. less than 200 wppm of overall impurities. Chlorine<30 wppm; organic material<30 wppm; water<30 wppm; and HCl<2° wppm; nonvolatile residue<60 wppm. Bromine dried by this process still contains a moisture level not low enough to prevent corrosion at elevated temperatures. Also, the process generates a dilute sulfuric acid solution which is a waste stream requiring disposal.
Thus, a need exists for processes and systems for drying liquid bromine without the use of drying agents and their attendant problems which is economical, results in two streams of high purity, dry bromine and substantially bromine-free water, and does not require additional environmental treatment of by-products.