The Thermodynamic and Kinetic Effects of Sodium Lignin Sulfonate on Ethylene Hydrate Formation

Abstract

Hydrate-based technologies (HBTs) have high potential in many fields. The industrial application of HBTs is limited by the low conversion rate of the water into hydrate (RWH), and sodium lignin sulfonate (SLS) has the potential to solve the above problem. In order to make the HBTs in the presence of SLS applied in industry and promote the advances of commercial HBTs, the effect of SLS on the thermodynamic equilibrium hydrate formation pressure (Peq) was investigated for the first time, and a new model (which can predict the Peq) was proposed to quantitatively describe the thermodynamic effect of SLS on the hydrate formation. Then, the effects of pressure and initial SLS concentration on the hydrate formation rate (rR) at different stages in the process of hydrate formation were investigated for the first time to reveal the kinetic effect of SLS on hydrate formation. The experimental results show that SLS caused little negative thermodynamic effect on hydrate formation. The Peq of the ethylene-SLS solution system predicted by the model proposed in this work matches the experimental data well, with an average relative deviation of 1.6% and a maximum relative deviation of 4.7%. SLS increased RWH: the final RWH increased from 57.6 ± 1.6% to higher than 70.0% by using SLS, and the highest final RWH (77.0 ± 2.1%) was achieved when the initial SLS concentration was 0.1 mass%. The rR did not significantly change as RWH increased from 35% to 65% in the formation process in the presence of SLS. The effect of increasing pressure on increasing rR decreased with the increase in RWH when RWH was lower than 30%, and the difference in pressure led to little difference in the rR when RWH was higher than 30%.