TY - JOUR

T1 - Urea as a green thermodynamic inhibitor of sII gas hydrates

AU - Gong, Yinghua

AU - Mendgaziev, Rais I.

AU - Hu, Wei

AU - Li, Yingzhou

AU - Li, Zhi

AU - Stoporev, Andrey S.

AU - Manakov, Andrey Yu

AU - Vinokurov, Vladimir A.

AU - Li, Tianduo

AU - Semenov, Anton P.

N1 - Funding Information: This work was supported by the Program for Scientific Research Innovation Team in Colleges and Universities of Shandong Province of Qilu University of Technology (Shandong Academy of Sciences), Young Taishan Scholar Program of Shandong Province (No. TSQN201909139), and National Natural Science Foundation of China ( 22073053 ). X-Ray study was funded by RFBR, project number 19-35-60013. Publisher Copyright: © 2021 Elsevier B.V.

PY - 2022/2/1

Y1 - 2022/2/1

N2 - This work is devoted to a systematic study of urea CO(NH2)2 as a promising and green gas hydrate inhibitor. The thermodynamic stability of sII gas hydrates forming from a binary gas mixture 4.34% C3H8 + 95.66% CH4 (mol%) in the presence of urea was analyzed. The hydrate equilibrium conditions were measured in a wide range of temperatures (267 – 294 K), pressures (0.9 – 9.4 MPa), and urea concentrations (0 – 50 mass%). The urea decreases the equilibrium temperature of sII hydrates formation, i.e., CO(NH2)2 acts as a thermodynamic hydrate inhibitor (THI). Powder X-ray diffraction at 173 K revealed the phases of sII gas hydrate, hexagonal ice, and tetragonal P4¯21m phase I urea. The determined parameter of sII hydrate unit cell (17.17 Å) indicates the non-inclusion of urea into the hydrate framework. An empirical correlation was proposed to describe the hydrate equilibrium temperature depression ΔTh depending on pressure and urea concentration. A linear relationship between ΔTh and a decrease in the ice freezing point ΔTice in urea aqueous solutions confirms the thermodynamic consistency of our data. Inhibition power of urea at 20 mass% and 6 MPa is 2 times less than that of methanol and is close to that for monoethylene glycol (MEG). In the range, up to 45 mass% urea is more effective THI than diethylene glycol (DEG). Urea is a less toxic compound compared to methanol and glycols, and also more cost-effective than MEG and DEG. Despite the medium anti-hydrate activity, urea can be considered as a safer for the environment hydrate inhibitor. Its application is justified if a shift of the hydrate equilibrium curve by no more than 10 – 12 K is required.

AB - This work is devoted to a systematic study of urea CO(NH2)2 as a promising and green gas hydrate inhibitor. The thermodynamic stability of sII gas hydrates forming from a binary gas mixture 4.34% C3H8 + 95.66% CH4 (mol%) in the presence of urea was analyzed. The hydrate equilibrium conditions were measured in a wide range of temperatures (267 – 294 K), pressures (0.9 – 9.4 MPa), and urea concentrations (0 – 50 mass%). The urea decreases the equilibrium temperature of sII hydrates formation, i.e., CO(NH2)2 acts as a thermodynamic hydrate inhibitor (THI). Powder X-ray diffraction at 173 K revealed the phases of sII gas hydrate, hexagonal ice, and tetragonal P4¯21m phase I urea. The determined parameter of sII hydrate unit cell (17.17 Å) indicates the non-inclusion of urea into the hydrate framework. An empirical correlation was proposed to describe the hydrate equilibrium temperature depression ΔTh depending on pressure and urea concentration. A linear relationship between ΔTh and a decrease in the ice freezing point ΔTice in urea aqueous solutions confirms the thermodynamic consistency of our data. Inhibition power of urea at 20 mass% and 6 MPa is 2 times less than that of methanol and is close to that for monoethylene glycol (MEG). In the range, up to 45 mass% urea is more effective THI than diethylene glycol (DEG). Urea is a less toxic compound compared to methanol and glycols, and also more cost-effective than MEG and DEG. Despite the medium anti-hydrate activity, urea can be considered as a safer for the environment hydrate inhibitor. Its application is justified if a shift of the hydrate equilibrium curve by no more than 10 – 12 K is required.

KW - Methane-propane gas mixture

KW - Phase equilibria

KW - Powder X-ray diffraction

KW - sII gas hydrates

KW - Thermodynamic hydrate inhibitor

KW - Urea

UR - http://www.scopus.com/inward/record.url?scp=85115436945&partnerID=8YFLogxK

U2 - 10.1016/j.cej.2021.132386

DO - 10.1016/j.cej.2021.132386

M3 - Article

AN - SCOPUS:85115436945

VL - 429

JO - Chemical Engineering Journal

JF - Chemical Engineering Journal

SN - 1385-8947

M1 - 132386

ER -