The term “sulfonation” is used when an electrophilic chemical reaction occurs in such a way that the SO3H functional group is attached to a molecule with the ability to donate electrons. If the electron donating molecule is carbon, the product of this chemical reaction is known as “sulfonic acid”. “Sulfation” reaction occurs when the functional group SO3H bonds to an oxygen atom in a carbon group to form a C-O-S sulfate group. Sulfate acids react quickly with moisture in the air; for this reason, the neutralization process should happen quickly after the formation of the sulfate group
Although sulfonation and sulfation processes are used industrially to produce a wide range of products, including hair dyes and insecticides, and their main application is in the production of anionic surfactants.
The sulfonation reaction can occur in different process structures. Structures including direct liquid-liquid contact or gas-liquid contact reactors. Also, different sulfonating agents can be used to complete this reaction: 1. Sulfuric acid – 2. Stabilized SO3 liquid – 3. SO3 gas created by sulfur fuel. In recent years, there has been a lot of favor for the sulfonation reaction based on direct gas-liquid contact (combination of air and SO3 gas with carbonic liquid), which may be due to the following reasons:
- Versatility – all types of carbon feeds such as: alkylbenzenes – primary alcohols – alcohol ethers – alpha olefins and fatty esters can be converted into high purity sulfonates or sulfates in this system.
- Process security – all other methods of producing sulfonates and sulfates (such as concentrated sulfuric acid) have low security for use in the process, storage, and transportation. In contrast, solid or liquid sulfur is less dangerous for producing SO3 gas.
- Price – SO3 gas produced from direct sulfur fuel is the most economical method of production, storage and transportation among the methods mentioned above.
- Availability – other types of sulfate and sulfonating agents are not easily available and cannot be produced easily.
The above schematic shows a sulfonation/sulfation process that occurs using SO3 gas. In the shown process, Bleaching step is also added, which is an optional step according to product characteristics and feed characteristics. Sulfonic acids produced by LAB do not require an aging step to complete the reaction.
