Abstract
Separation of HCl from the mixture of KCl and HCl using membrane distillation Membrane distillation (MD) was applied for the concentration of solutions containing hydrochloric acid and potassium chloride. The studies of the concentration and separation of HCl through the hydrophobic membrane were performed. In the investigations plate and frame or capillary modules, equipped with membranes from polytetrafluoroethylene and polypropylene were applied, respectively. The feed temperature amounted to 333 K or 343 K and permeate 293 K at the inlet of the module. Under the MD operation conditions the transfer of water vapour and hydrogen chloride from potassium chloride and hydrochloric acid solutions through the hydrophobic membranes took place, whereas the potassium chloride as a nonvolatile component underwent concentration in the feed. The influence of acid concentration and salt presence in the feed on the HCl molar flux through the membrane was systematically studied. The increase of the temperature and salt concentration in the feed caused higher partial pressure volatile of HCl and the resultant HCl Flux through a membrane was higher. During MD for the initial concentration in the feed equal 50 g KCl/dm3 and 40g HCl/dm3, at the feed temperature 343K, the permeate flux decreased from 353 dm3/m2d to 289 dm3/m2d, whereas the HCl flux increased to 6 mol/m2d for the capillary module. At higher KCl concentration in the feed, amounting to 100g KCl/dm3 and under the same operation conditions, the permeate flux decreased to 285 dm3/m2d, but the molar flux HCl increased to 18 mol/m2d. The results were compared with the data obtained for the plate and frame module.
Highlights
The membrane distillation (MD) process occurs when aqueous liquids with different temperature are separated by a hydrophobic membrane[1].The mechanism of separation in the MD process is associated with the equilibrium of the system feeding solution – vapour
The results of our work have shown a perspective for the MD application for the recovery of volatile hydrochloric acid from its solutions[3,4]
We have found that a high salt concentration causes HCl separation at acid concentration in the feed significantly lower than without the salt
Summary
The membrane distillation (MD) process occurs when aqueous liquids with different temperature are separated by a hydrophobic membrane[1]. The aim of the present work was to study the influence of salt concentration in HCl solutions on the separation of hydrochloric acid during membrane distillation. The vapour was condensed directly in the solution (distillate) in the cold compartment and HCl was dissolved. Tech., Vol 10, No 2, 2008 of HCl in the distillate every hour, taking into account the changes of the volume and the acid concentration in the distillate, according to the following equation: where ct and ct+1 are the distillate concentration at time t and t+1, Vt and Vt +1 are the volume of the distillate at time t and t+1, A is the membrane area inside the capillaries or the working area of the flat sheet membrane, M is the molar weight of HCl, and t is the time between the successive measurements
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