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What is Zinc bromide?
Zinc bromide is an inorganic bromide salt produced by the reaction of metallic zinc with bromine (or hydrobromic acid with zinc oxide). Its chemical formula is usually written as:
ZnBr2 (CAS No.: 7699-45-8, molecular weight approximately 225.2)
It is a white or colorless crystalline powder at room temperature, with a density of about 4.2 g/cm³, a melting point of about 394℃, and a boiling point of about 650~697℃. Zinc bromide is extremely hygroscopic and readily soluble in solvents such as water, alcohol, ether, and acetone, forming a high-density aqueous solution with good light transmittance.
Compositionally, zinc bromide consists of one zinc ion (Zn2+) and two bromide ions (Br-). The zinc ion can reversibly deposit/dissolve under an electric field, while the bromide ion can circulate between electrodes—this redox characteristic of the “zinc-bromine couple” is the chemical basis for the charge-discharge cycle of zinc-bromine flow batteries. The extremely high solubility of zinc bromide allows its aqueous solution to reach densities exceeding 2 g/cm³, which is the functional basis for its use as a high-density completion fluid and radiation shielding fluid in oil fields.
Chemically, zinc bromide is a mild Lewis acid that can catalyze a variety of organic reactions. Its solubility is superior to that of commonly used zinc chloride. It reacts with alkali metal hydroxides to form zinc hydroxide precipitate, which can be irritating to the skin. Due to its extreme hygroscopicity, it must be stored in a sealed, moisture-proof container.
Industrial-grade zinc bromide refers to products primarily intended for industrial production, with a purity generally exceeding 95% to 98%. Compared to reagent-grade and other specifications, industrial-grade products place greater emphasis on the following indicators:
Main content
Purity directly affects the density ratio of completion fluid, electrolyte performance and catalytic yield. Industrial grade generally requires a main content of over 95%.
Moisture
Zinc bromide is highly hygroscopic, and excessive moisture content can affect measurement accuracy and storage stability, so it must be strictly controlled and sealed in packaging.
Impurities (iron, copper, lead, calcium, etc.)
Impurities such as iron and copper can affect the corrosion resistance of the completion fluid and the charging and discharging efficiency of the electrolyte, and need to be controlled at a low level.
Water-insoluble matter
The completion fluid and shielding fluid must be clear and free of sediment, and water-insoluble matter must be strictly controlled.
Solution density and light transmittance
The application of brine in oilfields for radiation shielding has specific requirements for solution density and light transmittance, which are important performance indicators.
What are the applications of industrial-grade Zinc bromide?
1.Oilfield completion fluids and workover fluids (core applications)
Zinc bromide aqueous solution is a classic high-density, solid-free brine in the oil and gas industry, used for well completion, workover, perforation, and downhole operations. It relies on its high density to balance formation pressure and prevent blowouts, while being solid-free and not damaging to the reservoir. Global annual consumption reaches hundreds of millions of pounds, making it the largest industrial application of zinc bromide.
2.Zinc-bromine flow battery electrolyte
Water-based zinc bromide electrolyte is the core material of zinc-bromine flow battery (ZBFB). The battery uses the redox reaction of zinc-bromine redox couple to achieve charging and discharging. It has advantages such as low cost, high energy density, recyclable electrolyte and natural flame retardancy. It is an important technical route for grid-level energy storage and new energy peak shaving. Demonstration systems for user-side and oilfield scenarios have been built in China.
3.Organic synthesis catalysts
Zinc bromide is a mild Lewis acid catalyst with better solubility than zinc chloride. It is used to catalyze organic transformations such as carbonyl ene reactions (a key step in the synthesis of menthol from citronellol). Supported zinc bromide can also be used as a selective catalyst for the bromination of aromatic compounds and is also used in the research on the preparation of polymer electrolytes.
4.Rayon and Textile Finishing
Zinc bromide can be used as a finishing agent for rayon (viscose fiber) to improve fiber strength and processing performance, and has traditional applications in the textile industry.
5.Photography and video products (traditional applications, indirect contact)
Zinc bromide has a long history of use in imaging fields such as photographic emulsions, and the production of imaging products such as film and photographic paper may have involved bromide chemicals in the past.
6.Other Applications
Its applications extend to areas such as photographic emulsions, chemical analysis reagents, and the synthesis of fine chemicals, and its scope continues to expand.
Summarize
Zinc bromide is a white, highly hygroscopic, and water-soluble inorganic bromide salt. It has high density and solubility, and possesses both the redox activity of the zinc-bromine electrode and the catalytic ability of a Lewis acid. In daily life, we indirectly encounter it through supply chains such as oil and gas extraction, power grid energy storage, fragrances and flavors, rayon textiles, and photographic products. In industry, industrial-grade zinc bromide is widely used as a high-density completion and workover fluid in oil fields, an electrolyte in zinc-bromine flow batteries, a Lewis acid catalyst in organic synthesis, and a post-treatment agent for rayon. It is an important inorganic functional chemical bridging “daily use” and “energy, energy storage, and chemical industry.”
