A new hydrate-based recovery process for removing chlorinated hydrocarbons from aqueous solutions

Abstract

The main objective of this study was to check the feasibility of the newly proposed hydrate-based chlorinated hydrocarbon (CHC) recovery process for removing chlorinated hydrocarbons from aqueous solutions. Two key process variables of hydrate phase equilibria and formation kinetics were closely examined to develop the overall conceptual design of this technology. First, the ternary four-phase (H-L-W-L-CHC-V) hydrate equilibria of aqueous solutions containing methylene chloride (CH2Cl2), carbon tetrachloride (CCl4) 1,2-dichloroethane (CH2ClCH2Cl), 1,1,1-trichloroethane (CH3CCl3), and 1,1-dichloroethylene (CH2 = CCl2) were measured at various temperature and pressure conditions using three different types of help gases (CO2, N-2, CH4). The help gas + water + chlorinated hydrocarbons systems greatly reduced the hydrate-forming pressure, which confirmed the mixed hydrates with chlorinated hydrocarbons more stabilized than the simple hydrates consisting of a help gas and water. The degree of stabilization was found to follow the order of 1,2-dichloroethane < 1,1-dichloroethylene < methylene chloride <less than> 1,1,1-trichloroethane < carbon tetrachloride. For the N-2 + water + carbon tetrachloride system, the formation pressure reduction as much as 96% was observed at 279.35 K. Second, the formation kinetic experiments of carbon dioxide hydrates containing chlorinated hydrocarbons were conducted under isothermal and isobaric conditions. The consumption rate of carbon dioxide gas became fast at the early time of the growth period, gradually decreased, and finally went to the complete hydration. The proposed hydrate-based recovery process appears to be very simple from the operational point of view because no special facilities requiring sensitive and complex function are needed. Another advantage is that this process only requires carbon dioxide as a hydrate former. Best of all, this process can he applied to separation and recovery of other organic pollutants dissolved in aqueous solutions without changing the basic concept.