Crude oil production can be increased through Enhanced Oil Recovery (EOR) method, with chemical injection as one of the methods that can be used. Chemical injection is able to lower the value of interfacial tension (IFT) between oil and reservoir’s rock. Therefore, oil is able to flow out of rocks.

Surfactant is the chemical that plays the role of lowering the value of IFT. Petroleum sulfonate is the most common type of surfactant used in EOR method. MES is a surfactant that has surface-active properties, good biodegradability, good in detergency, and is not sensitive to water hardness. This study aims to perform sulfonation of methyl esters (ME) using SO₃ gas that is dissolved in oleum (H₂SO₄.SO₃). The methyl ester to be sulphonated is based on CNO and PKO. Sulfonation is performed in falling film reactor with a heating temperature of 70^oC and is equipped with cooling water to facilitate heat transfer. The product of sulfonation is tested by Fourier Transform Infra-Red (FTIR).

FTIR results indicate the presence of S=O and OH groups, indicating sulfonation reaction has occurred. The phase diagram test is performed to determine the composition between MES, cosurfactant, and water formation. The composition ratio of MES, cosurfactant, and briner water that is most isotropic is 1:20:27, with ethanol as the cosurfactant. The IFT test results showed that CNO type produces the lowest interfacial tension value against light oil and waxy oil, which is 11.4 mN/m and 10.3 mN /m respectively.