What are the zinc chloride manufacturing process

Zinc chloride manufacturing process is a series of chemical reactions to create the final product. This process is the basis for the majority of zinc chloride manufacturing plants and production in the world. There are two major types of zinc chloride production methods, which are called hydrochlorination and chlorination.

1.Hydrochlorination

 Is a process that takes place when hydrogen chloride reacts with metal oxide or metal ore containing zinc to form zinc chloride (ZnCl₂). However, this process also produces HCl gas as a byproduct which must be scrubbed from air after it is created and captured for disposal. The alternative method, chlorination (- IUPAC), does not produce any HCl gas because it uses elemental chlorine as its starting material instead of hydrogen chloride. It is the safest method of zinc chloride manufacturing and requires no scrubber. Chlorination has been the primary method used for zinc chloride production since 1985. It is also cheaper than hydrochlorination because elemental chlorine is less expensive than hydrogen chloride.

2.Chlorination

 This process takes place when elemental chlorine reacts with zinc ore or oxide to form metallic zinc and a mixture of chlorine gas (Cl) and other chlorinated gases called chlorides. The mixture of Cl and chlorides is then subjected to fractional distillation. The first distillation column produces a crude zinc chloride solution, or mother liquor, which is collected and sent to the second distillation column. The second distillation column separates the mother liquor into three fractions: ZnCl₂, hydrochloric acid (HCl), and sodium chloride. ZnCl₂ can be further purified by adding aqueous sodium hydroxide (NaOH) and passing it through a cation exchange column. This is one method of zinc chloride manufacturing process.

Physical properties of zinc chloride

1.Crystal structure

Crystal structure of zinc chloride is shown in the following figure. The red and blue spheres represent zinc and chloride ions respectively. Zinc chloride can also form a series of polymeric structures.

2.Melting point

The melting point of zinc chloride is 134.4 ℃. It does not melt at a single temperature, but instead melts over the range of 134 ℃ to 135 ℃ during cooling. The solidification occurs between -6 ℃ to 6 ℃ (21℉ to 43℉) at normal pressure and normal humidity level at room temperature and atmospheric pressure. The freezing/melting curve graph is shown in the following figure, which shows that its melting point is 134.4 ℃ and its freezing point is -6.4 ℃ (21F).

3.Density

The density of zinc chloride is 2.907 g/cm under 0 ℃, and the volume changes from that of a solid to a liquid. The specific gravity is 1.869 g/cm at 20 ℃. The relative density is 74% at 0 ℃ and 100% at 28.5 ℃.

4.Refractive index

The refractive index of zinc chloride is 1.3641 at 20 ℃, which indicates that it is a non-isotropic crystal material with low birefringence (less than 0.05). As the temperature increases, the refractive index drops from 1.3641 to 1.3382 at 50 ℃ and then rises again to 1.3654 at 298 ℃. The refractive index of zinc chloride is greater than that of water (1.333) at ordinary temperatures, so it has high birefringence on a microscopic scale as shown in the following figure.

5.Heat capacity

The heat capacity of zinc chloride is 30 J/gK so its thermal conductivity is low (0.648 W/mK).

6.Specific heat of zinc chloride

The specific heat of zinc chloride is (1.776 kJ/kgK) at 20 ℃, which means that it is an insulator and has high thermal diffusibility and virtually no thermal conductivity.

Uses of zinc chloride

1. Zinc chloride is an important raw material and intermediate used in the manufacture of other chemicals and in the production of popular products. It is used to make polymers, pigments, herbicides and pesticides such as ZnCl₂·4H₂O (killer), ZnCl₂·4HO (weed killer), etc. It is used for water treatment in domestic water treatment facilities and swimming pool sanitation.

2.Zinc chloride gas (CI) is also used to produce polychlorinated biphenyls (PCBs) .PCB is a group of man-made materials that are hazardous to human health and the environment, but they can also be useful as electrical insulating materials.

3. Zinc chloride has been used in the medical field as an antidote to some disease, such as zinc protoporphyrin (ZnPP), which is used to treat malaria.

4. Some people use zinc chloride-mineral water for medicinal purposes. For instance, Amalia Thorne in 1793 successfully treated syphilis with mineral water containing 22% zinc chloride-mineral water and 10% brine, but it was more effective when the proportion increased up to 25%.

In conclusions, zinc chloride manufacturing process mainly includes two steps: chlorination or hydrochlorination process and purification stage. Hydrochlorination (HCI) process produces hydrogen chloride gas as a byproduct, so it is more dangerous than chlorination process.