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1. Raw material preparation
In the production process of SLES, the most critical raw material is Lauryl Alcohol, which is a long-chain fatty alcohol obtained from natural oils or petroleum derivatives, usually with a C12 carbon chain. In addition, Ethylene Oxide and Sulfur Trioxide are required as core raw materials in sulfation and ethoxylation reactions.
2. Ethoxylation reaction
The first step is to ethoxylate lauryl alcohol to produce Lauryl Polyoxyethylene Ether (Laureth). This reaction is carried out by adding ethylene oxide to the hydroxyl group of lauryl alcohol under high pressure and high temperature conditions. The reaction formula of ethoxylation is as follows:
[ \text{C12H25OH} n(\text{CH2CH2O}) \rightarrow \text{C12H25(OCH2CH2)nOH} ]
Wherein, n represents the number of ethoxy units added, usually between 2 and 3. The number of ethoxy units can be adjusted by controlling the reaction conditions during production, which will affect the properties of SLES, such as its surface activity and solubility.
3. Sulfation reaction
Next, lauryl alcohol polyoxyethylene ether is subjected to a sulfation reaction with sulfur trioxide (SO3) to produce laureth sulfate. This process is usually carried out in a continuous sulfation reactor. During the reaction, SO3 gas needs to be introduced into the reactor. The reaction formula is as follows:
[ \text{C12H25(OCH2CH2)nOH} SO3 \rightarrow \text{C12H25(OCH2CH2)nOSO3H} ]
This is an exothermic reaction, so temperature control is very important, usually between 40-60 degrees Celsius. In order to prevent the occurrence of side reactions, a certain negative pressure is maintained in the reactor.
4. Neutralization reaction
The product after sulfation is an acidic compound Laureth Sulfate Acid, so it needs to be neutralized with an alkaline substance. Typically, sodium hydroxide (NaOH) or sodium carbonate (Na2CO3) is used for neutralization to produce the final SLES:
[ \text{C12H25(OCH2CH2)nOSO3H} NaOH \rightarrow \text{C12H25(OCH2CH2)nOSO3Na} H2O ]
At this point, SLES has been formed, and the chemical formula is:
[ \text{C12H25(OCH2CH2)nOSO3Na} ]
5. Post-treatment and concentration
The SLES solution generated by the reaction is usually low-concentration, so it needs to be concentrated. By evaporating excess water, the concentration of SLES can be increased to about 70%, which is a common concentration standard for industrial-grade SLES products.
6. Stabilizer addition and product adjustment
In the concentrated SLES solution, some stabilizers and preservatives are usually added to prevent the product from degrading or deteriorating during storage. These stabilizers may include dimethylsiloxane or other types of antioxidants. Manufacturers may also adjust the color, smell and viscosity of SLES according to customer needs.
7. Quality Testing
In the final stage of production, SLES needs to undergo strict quality testing. The testing content usually includes:
- pH value: usually controlled between 6-8.
- Active matter content: usually controlled between 28-70%, depending on the product use.
- Appearance: requires no obvious impurities and a uniform solution.
- Heavy metal content: ensure compliance with safety standards, especially the detection of harmful elements such as cadmium and lead.
8. Packaging and storage
Qualified SLES products will be packaged in liquid or powder form and stored in sealed containers to avoid the influence of moisture and air. Usually, liquid SLES is stored in stainless steel tanks, while powdered SLES is packaged in moisture-proof bags for transportation and use.