Aluminium Chloride

Brief Overview

Aluminium chloride, AlCl₃, is well-known as a catalyst for organic reactions. This compound is soluble in water, hydrogen chloride, ethanol, chloroform, CCl₄ and is slightly soluble in benzene. It is a silver-white powder but sometimes turns to yellow if it is contaminated by ferric chloride. It tends to absorb water easily (hygroscopic) to form monohydrate or hexahydrate. Aluminium chloride is a corrosive substance and it is also very toxic. It can cause high damage to the eyes, skin, and respiratory systems if inhaled or upon contact.

Aluminium chloride is widely used for Friedel-Crafts reaction as a catalyst. AlCl₃ works as an electron acceptor (Lewis Acid). AlCl₃ is able to direct the reaction more efficiently and effectively. This catalyst is used to synthesize alkyl benzene from alkyl halide and benzene. It is also used for many industrial applications such as petrochemical manufacture, pharmaceuticals, dyes intermediates, and other organic chemicals. Moreover, it can be used for the metallurgical industry, cosmetics, antiperspirants, metallurgical industry, and lubricants.

Manufacturing Process

There are mainly two ways of synthesis: manufacturing aluminium chloride with chlorine or hydrogen chloride, or obtaining aluminium chloride by extraction from raw materials. In the former method, aluminium chloride is widely manufactured by reacting with an aluminium metal with chlorine or hydrogen chloride. This reaction occurs at a temperature ranging from 650 to 750°C and is classified as an exothermic reaction. In the latter method, to produce aluminium chloride, the aluminium metals can be extracted from raw material, such as clay or fly ash.

The preferred method of preparing anhydrous aluminium chloride comprises the steps of:

1. Alumina raw materials, such as clay, undergo the drying and calcining process to activate the alumina fraction for HCl leaching;
2. Dissolving the alumina fraction into soluble aluminium chloride by HCl leaching of calcined clay.
3. Solid/liquid separation to obtain remove all the solid that still contain in aluminium chloride solution, typically by the use of settlers and/or filters;
4. Separation of any soluble iron chloride from process liquor;
5. Crystallization of filtrate to separate slurry from aluminium chloride hexahydrate crystals;
6. Heating the aluminium chloride hexahydrate crystals to a temperature up to about 450°C.
7. Reducing aluminium chloride hexahydrate crystals to form anhydrous aluminium chloride.

Other ways of manufacturing aluminium chloride are:

• Reaction of aluminum metal in a heated stream of hydrochloric acid gas

                                                                          2 Al + 6 HCl → 2 AlCl₃ + 3 H₂

• Reaction of bauxite with coke and chlorine at about 875°C
• Catalytic chlorination of gamma-alumina in a fluidized bed
   

Metallurgy Industry

Aluminium chloride is used to make aluminium metal. Due to its explosive reaction upon contact with water, it requires care in such situations. It can be combined with aluminium as a catalyst to synthesize metal complexes using a process called Fisher-Hafner synthesis. The primary components of this reaction are metal halides. Besides, aluminium chloride is also applied as a flux and in the electrolytic production of aluminium melting. It is also necessary for the manufacturing of titanium dioxide and butyl rubber.

Detergent Industry

It is used in the process of manufacturing dodecylbenzene, a colorless liquid which is a precursor to sodium dodecylbenzenesulfonate, an important component (15%) in laundry detergent. In the process of manufacturing sodium dodecylbenzenesulfonate for the laundry industry, AlCl3 acts as an acid catalyst when alkene is reacted with excess benzene to form alkyl benzene compound. The resulting mixture is sulfonated to produce sulfonic acid which is neutralized with alkali to give sodium dodecylbenzenesulfonate.

Intermediate Chemicals

The most important aluminium chloride in a chemical reaction is its role as a catalyst in Friedel-Crafts reactions. In these reactions, aluminum chloride is used to prepare anthraquinone, which is used in the dyestuffs industry. Aluminium chloride is also used to insert aldehyde groups in aromatic system rings, the general process used for this is the Gattermann-Koch reaction. AlCl3 acts as a catalyst in the “ene –reaction” and is used in the manufacturing of polystyrene. AlCl3 alkylation process produces chemicals that are used in the production of detergents and ethylbenzene.

Petrochemical Industry

Aluminium chloride is utilized for the isomerization and compounding of hydrocarbons and supports in the polymerization of hydrocarbons with lighter molecular weight, the compound is mainly used in the petrochemical industry.

Drug Industry

Aluminium chloride is a medication that treats severe, recalcitrant excessive sweating (hyperhidrosis).

Wastewater Treatment

Aluminium chloride is used as a coagulant for many industrial and sanitary wastewater treatment applications, because of its high efficiency, effectiveness in clarification, and utility as a sludge dewatering agent. The chemical leaves no residual color and offers very good turbidity removal.

Hydrated Aluminium Chloride

The hexahydrate form of aluminium chloride has little applications, usually as a component in many cosmetic products and toiletries. Hydrated aluminium chloride is often applied in low concentrations in antiperspirants. Prescription products used to control hyperhidrosis have a higher concentration of the compound. There have also been clinical trials to understand the impact of aluminium chloride used in anti-acne preparations.

Other Applications

Aluminium chloride is used for cracking of petroleum, manufacturing of parchment paper, rubbers and lubricants, preserving wood, disinfecting stables and slaughterhouses, preparing deodorants and antiperspirants, refining crude oil, and dyeing fabrics.