Removal of Aromatic Hydrocarbon Compounds by Hydroxypropyl-cyclodextrin

Area of Science:

• Environmental Chemistry
• Organic Chemistry
• Remediation Technologies

Background:

• Activated carbon is effective for removing benzene, toluene, and xylenes (BTEX) from air and water.
• Soil remediation of BTEX compounds remains challenging due to their low apparent solubility.
• Increasing the apparent solubility of organic compounds in soil is a key strategy for BTEX removal.

Purpose of the Study:

• To investigate the apparent solubilities of benzene, toluene, and xylenes.
• To estimate the inclusion behavior of BTEX compounds into natural cyclodextrins (CDs) and hydroxypropyl-cyclodextrins (HP-CDs).
• To evaluate the potential of cyclodextrins for enhancing BTEX solubility in liquid phases for soil remediation.

Main Methods:

• Measurement of apparent solubilities of benzene, toluene, and xylenes in aqueous solutions.
• Comparison of solubility enhancement using natural cyclodextrins (CDs) versus hydroxypropyl-cyclodextrins (HP-CDs).
• Analysis of factors influencing BTEX inclusion in HP-CDs, including molecular diameter, CD cavity size, and partition coefficients.

Main Results:

• Natural CDs did not significantly increase the apparent solubilities of benzene, toluene, and xylenes.
• HP-CDs markedly increased the apparent solubilities of benzene, toluene, and xylenes.
• The solubility enhancement of BTEX in HP-CD solutions correlated with molecular size, CD cavity dimensions, and the 1-octanol-water partition coefficient.
• p-Xylene exhibited higher solubility than o-xylene and m-xylene due to reduced steric hindrance.

Conclusions:

• HP-CDs are effective in increasing the apparent solubilities of benzene, toluene, and xylenes in aqueous solutions.
• The inclusion mechanism of BTEX in HP-CDs is influenced by steric and hydrophobic interactions.
• HP-CDs show promise as a viable method for enhancing the removal of BTEX compounds from contaminated soils.