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

The main objective of this study was to check the feasibility of the newly proposed hydrate-based chlorinated hydrocarbon (CHC) recovery process for r emoving chlorinated hydrocarbons from aqueous solutions. Two key process va riables of hydrate phase equilibria and formation kinetics were closely exa mined to develop the overall conceptual design of this technology. First, t he ternary four-phase (H-L-W-L-CHC-V) hydrate equilibria of aqueous solutio ns containing methylene chloride (CH2Cl2), carbon tetrachloride (CCl4) 1,2- dichloroethane (CH2ClCH2Cl), 1,1,1-trichloroethane (CH3CCl3), and 1,1-dichl oroethylene (CH2 = CCl2) were measured at various temperature and pressure conditions using three different types of help gases (CO2, N-2, CH4). The h elp gas + water + chlorinated hydrocarbons systems greatly reduced the hydr ate-forming pressure, which confirmed the mixed hydrates with chlorinated h ydrocarbons more stabilized than the simple hydrates consisting of a help g as 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 o bserved at 279.35 K. Second, the formation kinetic experiments of carbon di oxide hydrates containing chlorinated hydrocarbons were conducted under iso thermal and isobaric conditions. The consumption rate of carbon dioxide gas became fast at the early time of the growth period, gradually decreased, a nd finally went to the complete hydration. The proposed hydrate-based recov ery process appears to be very simple from the operational point of view be cause no special facilities requiring sensitive and complex function are ne eded. Another advantage is that this process only requires carbon dioxide a s a hydrate former. Best of all, this process can he applied to separation and recovery of other organic pollutants dissolved in aqueous solutions wit hout changing the basic concept.