What Is Lithium Bromide?

Lithium bromide, molecular formula: LiBr. White cubic crystal or granular powder, easily soluble in water, soluble in ethanol and ether, slightly soluble in pyridine, soluble in organic solvents such as methanol, acetone and ethylene glycol. It is an efficient water vapor absorbent and air humidity regulator. It can be used as absorption refrigerant, hydrogen chloride removing agent in organic chemistry, fiber fluffing agent, hypnotic agent and sedative agent in medicine, and also used in photosensitive industry, analytical chemical reagent and electrolyte in some high-energy batteries.

1. Properties: white powder or granular crystal, which belongs to cubic crystal system. Colorless transparent or light yellow liquid.

2. Density (g / mL, 25/4 ° C): 3.464.

3. Melting point (ºC): 442 547.

5. Boiling point (ºC, atmospheric pressure): 1265.

19. Solubility: soluble in water, ethanol and ether; slightly soluble in pyridine; soluble in organic solvents such as methanol, acetone and ethylene glycol.

1. Reference value for calculation of hydrophobic parameters (XlogP): None

2. Number of hydrogen-bonded donors: 0

3. Number of hydrogen bond acceptors: 1

4. Number of rotatable chemical bonds: 0

5. Number of tautomers: none

6. Topological molecular polar surface area: 80.3

7, the number of heavy atoms: 2

8. Surface charge: 0

9. Complexity: 2

10. Number of isotope atoms: 0

11. Determine the number of atomic stereocenters: 0

12. Uncertain number of atomic stereocenters: 0

13. Determine the number of chemical bond stereocenters: 0

14. Uncertain number of chemical bond stereocenters: 0

15. Number of covalent bond units: 2 ^[1]

It is stable in nature, and it is not easy to deteriorate and decompose in the atmosphere. With ammonia or amines

1. Neutralization method

A neutralization reaction between lithium hydroxide and hydrobromic acid is performed, and the reaction solution is decolorized, filtered, and the filtrate is concentrated, filtered, concentrated, crystallized, and separated to obtain a lithium bromide granular powder product. The reaction equation is as follows:

LiOH + HBr = LiBr + H ₂ O

2.Iron bromide method

The iron filings are reacted with bromine to form iron bromide, and then lithium carbonate is produced by the action of lithium carbonate and iron bromide. The process of this method is complicated, and it is easy to cause the loss of lithium bromide and reduce the yield.

3. Dissolve the pure lithium carbonate in the hydrobromic acid solution, evaporate to dryness, and remove the CO ₂ and water to obtain lithium bromide.

If particularly pure lithium bromide is to be prepared, it can be recrystallized several times to remove most impurities. The specific operation is as follows: Hydrobromic acid is added to the LiBr solution to precipitate lithium bromide. The above solution and precipitate were heated while passing nitrogen to remove excess acid. The precipitate was filtered off under a nitrogen atmosphere. Lithium bromide is used to recrystallize at a large difference in solubility in water at different temperatures, and the recrystallization is repeated 4 to 5 times. Finally, the platinum lithium container was kept at 160 ° C. for more than 7 days in a nitrogen atmosphere, and the purified lithium bromide was sealed in a glass tube and stored.

4. First prepare lithium carbonate into a 55% to 60% solution, and slowly add a slight excess of 45% hydrobromic acid to the reaction under constant heating and stirring:

Li ₂ CO ₃ + 2HBr = 2LiBr + CO ₂ + H ₂ O

After the reaction, the insoluble matter was filtered off, the filtrate was concentrated by heating until a small amount of crystals appeared, the heating was stopped, and the crystals were cooled. After the crystallization was completed, the mother liquor was separated, dried and dehydrated to obtain the finished product. Mother liquor can be re-concentrated and crystallized ^[2]

1. It should be stored in a ventilated and dry warehouse.

2. The packaging should be sealed and moisture-proof. Protect from rain and sunlight during transportation.

Large doses of lithium bromide inhibit

Is a highly efficient water vapor absorbent and air humidity regulator. The refrigeration industry is widely used as

(1) A colorless liquid with a salty taste and non-toxicity. The solution is pale yellow after adding lithium chromate.

(2) The solubility of lithium bromide in water decreases with decreasing temperature. As shown in Figure 1. The curve in the figure is a crystallization line. The points on the curve indicate that the solution is in a saturated state. The upper left of the curve indicates the precipitation of solid lithium bromide crystals, and the lower right indicates that there are no crystals in the solution. The so-called solubility refers to the mass component of the lithium bromide anhydrous compound contained in the saturated liquid, that is, the mass concentration of the lithium bromide aqueous solution. From the curve in the figure, it can be known that the mass concentration of lithium bromide should not exceed 66%, otherwise crystals will precipitate when the temperature of the solution decreases during operation, which will damage the normal operation of the refrigerator.

(3) The partial pressure of water vapor is very low, and it is much lower than the saturated vapor pressure of pure water at the same temperature, so it has strong hygroscopicity. The balance between liquid and vapor belongs to dynamic equilibrium. At this time, the rate at which molecules cross the surface of the liquid into the vapor is equal to the rate at which the molecules return from the vapor to the liquid. Because the attractiveness of lithium bromide molecules to water molecules in lithium bromide solution is stronger than that between water molecules, and because the number of water molecules is reduced by the presence of lithium bromide molecules in a unit liquid volume, the liquid at the same temperature The number of water molecules per unit volume of steam on the surface is less than the number of water molecules on the surface of pure water. Because lithium bromide has a high boiling point and does not volatilize in the temperature range used, the total pressure of the vapor in equilibrium with the solution is equal to the pressure of water vapor. It can be seen that the water vapor content on the surface of the lithium bromide solution is equal when the temperature is equal. The pressure is less than the saturated vapor pressure of pure water, and the higher the concentration or the lower the temperature, the lower the partial pressure of water vapor. Figure 2 shows the relationship between the temperature, concentration and pressure of a lithium bromide solution. As can be seen from the figure, when the concentration is 50% and the temperature is 25 ° C, the saturated vapor pressure is 0.85kPa, and the saturated vapor pressure of water at the same temperature is 3.167kPa. If the saturated vapor pressure of water is greater than 0.85kPa, for example, when the pressure is 1kPa (equivalent to a saturation temperature of 7 ° C), the above lithium bromide solution has the ability to absorb it, which means that the aqueous lithium bromide solution has a water vapor absorption temperature lower than it Capacity, this is one of the mechanisms of the lithium bromide absorption refrigerator. Similarly, if the pressure is the same, the saturation temperature of the solution must be greater than the saturation temperature of water, and the water vapor generated in the solution is always in a superheated state.

(4) The density is greater than that of water and varies with the concentration and temperature of the solution.

(5) The specific heat capacity is small. When the temperature is 150 ° C and the concentration is 55%, the specific heat capacity is about 2kJ / (kg · K), which means that less heat is added to the solution during the occurrence process, and the feature that the latent heat of evaporation is relatively large , Will make the unit have a higher thermal coefficient.

(6) The viscosity is large.

(7) The surface tension is large.

(8) The thermal conductivity of aqueous lithium bromide solution decreases with increasing concentration and increases with increasing temperature.

(9) It is strongly corrosive to ferrous metals, copper and other materials. It is more serious in the presence of air. The non-condensable gas generated by corrosion has a great impact on the refrigeration capacity of the device.

The main disadvantages of the absorption refrigeration system when working with lithium bromide aqueous solution are: low thermal efficiency, large cooling water consumption, high requirements for tightness of the equipment, and a certain degree of corrosion. But because it can directly use low-parameter heat sources as power, it is an ideal refrigeration device using solar low-grade heat sources. Except for the small-power canned motor pump, the entire unit has no other moving parts and runs quietly. There is basically no noise and Vibration; Lithium bromide ~ water as working medium pair, non-toxic, odorless, and help to meet environmental protection requirements; the refrigerator is carried out in a vacuum state, there is no danger of high-pressure explosion; the cooling capacity can be adjusted in a wide range, at 20% to 100% The cooling capacity can be adjusted steplessly; it has strong adaptability to changes in external conditions. It can be used under heating steam pressure of 0.2 to 0.8 MPa (gauge pressure), cooling water temperature of 20 to 35 ° C, and refrigerant water outlet temperature of 5 to 15 ° C. Stable operation within the scope of the unit; simple structure of the unit, low requirements for the installation foundation, no special machine base required; small size, land saving, easy manufacturing management, low maintenance costs, and very safe operation.

Lithium bromide solution is used as a working medium to produce low-temperature refrigerant water. It is used as a cold source in air-conditioning systems and processes. It can be widely used in industrial and mining enterprises such as textiles, chemicals, electronics, food, etc. , Buildings, etc.