Investigation of nonylphenol ethoxylate on the surface characteristics of low rank coal

Abstract

The surface characteristics of sub-bituminous coal have been determined in the presence of nonylphenol ethoxylate with 9 ethylene oxide groups (NP-9). The surface characterization techniques of zeta potential measurement, contact angle measurement, and surfactant adsorption have been used. Addition of NP-9 causes the zeta potential profiles to become less negative resulting from the surfactant molecules shielding the negative charge of the sub-bituminous coal. Changes in the sub-bituminous coal surface hydrophobicity are assessed using contact angle measurements. As the concentration of NP-9 gradually increases, the contact angle first increases and then decreases with the maximum contact angle at about critical micelle concentration (CMC) of NP-9. FTIR and XPS results show that oxygen functional groups on the low-rank coal surface were significantly covered by the NP-9, which indicates more hydrophobicity for the low-rank coal after adsorbing surfactant. The surfactant adsorption has been investigated as a function of concentration and temperature. The adsorption isotherms are well fitted by the Langmuir equation. The adsorption data are utilized to calculate thermodynamic parameters. The thermodynamic functions indicate that the whole adsorption process is exothermic, being driven by enthalpy-entropy synergically.

Keywords:

• Sub-bituminous coal
• nonylphenol ethoxylate
• adsorption
• contact angle
• hydrophobicity

Additional information

Funding

This work was supported by the SDUST Research Fund under Grant number [2018TDJH101].