Concentration of Mechanical Pulp Mill Effluents and NaCl Solutions through Propane Hydrate Formation

In this work, recovery of water from mechanical pulp mill effluents and 2.5 wt % NaCl solutions through propane hydrate formation was investigated. A new apparatus in which hydrate nucleation, growth, separation, and melting occur in one vessel was designed and built. The emphasis of the work was on crystal separation. The average reduction in the salt content of the recovered water from the NaCl solutions was found to be 31%. Displacement with propane could increase the amount of recovered water at the same purity level. Further improvement in the purity could be accomplished with washing with water. The results with the effluents showed that the total organic carbon and the salt content of the recovered water were lower by 23 and 26%, respectively, from the levels in the effluent. Improved separation could be achieved by displacement with liquid propane.