Synthesis of Cu-Al LDH nanofluid and effectiveness as a promoter for CO2 hydrate formation

The present study focuses on the synthesis of a hybrid nanofluid (Cu-Al LDH) and the investigation of its effectiveness as a promoter for CO2 hydrate formation. The Cu-Al LDH nanofluid has been prepared using the one-step co-precipitation technique. XRD (X-ray diffraction) and TEM (transmission electron microscopy) analyses have been carried out to evaluate the structural features and particle size measurement. The stability of nanofluid is evaluated using zeta potential measurements. The hydrate formation experiments are conducted in a pilot-scale reactor of 25 L volume with a design pressure of 180 bar. The wall temperature of the reactor is set at 2 °C. The charging of the reactor is carried out in both single and dual-stage at the maximum pressure of 30 bar. The results on the enhancement of gas absorption, total gas consumption, and water to hydrate conversion compared to pure water are reported. Parametric study on the effect of Cu-Al LDH nanofluid concentrations (0.25, 0.5, and 1.0 wt%) and molar ratios (Cu2+:Al3+: Na+ = 4:1:4 and 4:1:4.7) have been carried out. The gas absorption process is more sensitive to molar ratio than the concentration of LDH nanofluid, and about 20 times increase in absorption takes place due to LDH nanofluid in dual gas charging mode. The shuttle effect of the nanoparticle is primarily attributed to the increase in CO2 gas absorption. The strength of gas absorption influences the hydrate morphology. Accordingly, hydrate formation is initiated from the gas–liquid interface in low CO2 absorption case, and hydrate slurry formation inside the bulk fluid followed by layer-wise growth of hydrate from the interface takes place in high gas absorption case. Maximum 176.19% increase in gas consumption is observed at 0.5 wt% nanofluid concentration for (Cu2+:Al3+: Na+ = 4:1:4.7) molar ratio compared to pure water.