Sulphonation

Sulphonation is key to making the sulfates used as key ingredients in soaps and detergents, and manufactured in a process called “Sulphonation”.

Production Process

Fundamentally, Sulphonation is based on the reaction between a sulphur trioxide stream diluted in air and an organic base. The reaction is carried out in a stainless-steel multi-tube film reactor where the sulphur trioxide stream and the organic base are conveyed in co-current, for a reaction time necessary for a sulphuric group to react with the base and to form an additioned molecule. This molecule has an electrically neutral end (the hydrocarbon chain), which is hydrophobic, and a hydrophilic polar end (the sulphuric group). This dual property is the key behind the detergent behavior of the LABSA (linear alkyl benzene sulphonic acid), and its ability to modify the water surface tension

Product quality control

Color is a critical property for the commercial value of the sulphonated organic base. Color may be impaired by several factors, including reaction temperature. Since the reaction is fairly exothermal, in order to hold constant temperature, the reactor tube bundle is submerged in circulating cooling water under temperature control. Sulphuric acid content, free oil content, and density are other quantifiable parameters of product quality.

Common section of the production process

The sulphuric stream production is a common feature of all sulphonation processes. The sulphuric stream is manufactured by a process similar to the sulphuric acid (H2SO4) production. Solid Sulphur is the raw material, usually in pellet form at high purity as produced by the Claus process, which is the partial oxidation of sour gas, any gas such as natural gas with a significant amount of hydrogen sulfide. Sulphur is molten by steam in a jacketed tank, then is pumped to a combustion furnace where is burnt in a large excess of air with formation of sulphur dioxide. It is critical for the sulphur dioxide stream to be cooled down for the next processing step.

Conversion and sulphonation

The cooled down Sulphur dioxide is then conveyed to a multi-layer catalytic reactor, where sulphur dioxide (SO2) is converted almost completely to sulphur trioxide (SO3). Further cooling and filtration of this stream is required before being reacted with the organic base in the multi-tube film reactor.

Under strict control of temperature and of flow rate, the organic base is fed to the sulphonation reactor. Software and hardware enable the operator to carry out the control tasks automatically or flexibly bring such key parameters under manual control.

SLES (sulphonated ethoxylated lauryl alcohol)

A LESA (type of acid) stream is neutralized in a loop where the reactor output is treated with a caustic soda solution and is subject to a homogenizing process in a dedicated piece of equipment achieving lump-free and stringent homogenization specifications as necessary for its application in the cosmetic industry. A special cooler is used to handle the significant amount of heat developing out of the neutralization reaction; then, for color adjustment, pH adjustment, deareation and product ageing -- additional on-stream equipment and injections are used. Deareation consists in the removal of small air bubbles forming during the various atmospheric processes, in a degasifier working under vacuum, providing a crystal appearance to the SLES paste.

1,4 – Dioxane, eventually produced as an undesired by-product of the sulphonation reaction, can be removed by further optional treatment. Dioxane is stripped out of the paste in a vacuum film evaporator where also deareation occurs simultaneously.

AOS (sodium alpha olefin sulfonate)

A supplementary treatment is involved in the production of Sodium Alpha Olefin Sulfonate (AOS), named “hydrolysis”, in addition to the neutralization of caustic soda from the acidic reactor output. The neutralized AOS stream is heated up to high temperature, homogenized and aged per proper time specifications ensuring the complete conversion of Sultones to surfactant compounds. After a final cooling, the product is ready for storage or packing.

Technology providers:

• Chemithon
• Desmet Ballestra
• Lion Corp
• Marsina Engineering
• Mazzoni
• Meccaniche Modeme

Fatty Acid & Glycerin Production

Another critical part of the soap supply chain is oleochemical plants. Please find the below link to learn more about fatty acid and glycerin production.

https://www.phxequip.com/resource-detail.64/edible-oils-fats-refining-process.aspx

Conclusion

Proper attention to production parameter is key to the quality of the intermediaries produced in the sulphonation process. It might be best to consult with multiple technology providers to get the results your customers require.