Kinetic Gas Hydrate Inhibition by Alternating Dipeptoids with Optimal Size and Shape N-Substituents

Area of Science:

• Materials Science
• Chemical Engineering
• Polymer Chemistry

Background:

• Commercial kinetic hydrate inhibitors (KHIs) rely on water-soluble polymers with amphiphilic groups.
• Hydrophobic moiety size and shape are crucial for KHI efficacy.
• Proteins and peptides offer an environmentally friendly, bioengineerable KHI alternative.

Purpose of the Study:

• To explore novel alternating dipeptoid polymers as kinetic hydrate inhibitors.
• To investigate the impact of alkyl side chain size and shape on KHI performance.
• To evaluate the potential of glycine-derived dipeptoids as sustainable KHIs.

Main Methods:

• Synthesis of alternating dipeptoids with glycine and varying alkyl side chains.
• High-pressure steel rocking cell experiments using the slow constant cooling (SCC) test method (1 °C/h).
• Testing with a synthetic natural gas mixture to assess kinetic hydrate inhibition.

Main Results:

• All synthesized dipeptoids demonstrated good KHI performance.
• The dipeptoid with a glycine-N-propylleucine repeating unit (Poly iC4-Pr), featuring pendant iso-butyl groups, showed optimal performance, matching poly(N-vinyl caprolactam).
• Dipeptoids with smaller or larger alkyl groups exhibited reduced KHI efficacy, suggesting iso-butyl is an optimal hydrophobic moiety size.

Conclusions:

• The iso-butyl group is conjectured to be the optimal size for this class of dipeptoid KHIs.
• Optimal KHI performance requires amphiphilic groups with specific hydrophobic moiety size and shape adjacent to hydrogen-bonding groups.
• The solvent n-butyl glycol ether acts as a synergist, further enhancing the performance of Poly iC4-Pr.