A green approach to hydrate control in sour natural gas: Evaluating Urea as a thermodynamic inhibitor

Purpose: Gas hydrates in sour natural gas containing H۲S pose critical flow-assurance risks. Conventional thermodynamic inhibitors work but raise environmental and regeneration concerns. Urea, a biodegradable candidate, has been little studied for sour systems. This work experimentally determines three-phase equilibrium (V–Lw–H) for a representative sour mixture (CH۴ + C۳H۸ + H۲S) with ۰–۵۰ wt% urea, and compares the results with (i) literature data for a sweet CH۴ + C۳H۸ system and (ii) ۲۰ wt% monoethylene glycol (MEG) for the same sour gas. Methods: Experiments used a stirred high-pressure autoclave under isochoric T-cycle conditions. Temperature and pressure accuracies were ±۰.۱۰ K and ±۰.۱۳ MPa. Urea solutions (۰–۵۰ wt%) in deionized water were tested, and equilibrium identified by slow-heating dissociation. The same setup and gas composition benchmarked against previously measured MEG ۲۰ wt% data. Results: Urea acted as an effective THI, shifting the hydrate equilibrium to lower temperatures across ۲.۲۹–۱۲.۰۸ MPa. The equilibrium-temperature depression ΔTₕ increased with concentration, reaching ≈۱۳ K at ۵۰ wt%. At ۲۰ wt%, urea produced ΔTₕ ≈ ۴.۵۱ K (at matched pressures), whereas MEG ۲۰ wt% yielded an average ΔTₕ ≈ ۵.۶۰ K, i.e., ~۱.۱ K stronger suppression. The ΔTₕ–concentration trend was nearly linear up to ۳۰–۴۰ wt%, followed by mild leveling, and agreed in magnitude and slope with published sweet-gas (CH۴ + C۳H۸) results, indicating that H۲S does not materially diminish urea efficacy within the studied range. Conclusion: This fully experimental study demonstrates that urea is a viable green thermodynamic inhibitor for sour natural gas hydrates, providing moderate, concentration-dependent suppression (≤۱۰–۱۳ K) with reproducible results. While MEG ۲۰ wt% is ~۱ K stronger, urea offers comparable inhibition and better environmental attributes, supporting its practical use where moderate temperature shifts meet design requirements.

کلیدواژه ها:

Gas hydrates ، Sour natural gas ، Thermodynamic inhibitor ، Urea ، Monoethylene glycol ، Isochoric T-cycle