Clathrate hydrate dissociation conditions for refrigerant + sucrose aqueous solution: Experimental measurement and thermodynamic modelling

It has been shown in literature that gas hydrates can be used in sugar milling processes as a means of increasing the solids content in aqueous carbohydrate systems. In order to fully understand the practicalities of using gas hydrate technology in this regard, it is important to accurately know hydrate formation/dissociation conditions. The aim of this study is to obtain hydrate dissociation conditions of various refrigerant hydrates in the presence of sucrose aqueous solutions. The data will be used to design an aqueous solution separation process. The measurements were performed using the isochoric pressure search method with a newly developed high-pressure apparatus. New experimental gas hydrate systems measured include R134a + water + (12 or 15) weight percent sucrose, R410a + water + (12 or 15) weight percent sucrose, and R507 + water + (12 or 15) weight percent sucrose. Measurements were undertaken in the temperature range between (276.5 and 289.1) K and pressures ranging from (0.136-0.962) MPa. In addition, a sucrose sample supplied by the Sugar Milling Research Institute (SMRI) in Durban, South Africa was also investigated. The results show that the presence of sucrose exhibits an inhibition effect on hydrate formation. This is seen by the shift of the equilibrium phase boundary to either higher pressures or lower temperatures. Additionally, through measurements performed on the SMRI sample it can be seen that the presence of additional carbohydrates (glucose and fructose) in the system increases the effect of inhibition on hydrate formation. A thermodynamic model based on the van der Waals-Platteeuw solid solution theory was used to model the hydrate dissociation conditions. A good agreement between the experimental measurements and the model was observed.