Membrane condenser as emerging technology for resources recovery and environment protection

Nowadays the availability of potable water has become an environmental issue due to the continuous growth in water demand not balanced by an adequate recharge. Up to now, much effort has been put in cleaning methods for waste water treatment. In contrast, there are always huge quantities of water emitted in the air. The new stringent rules on emissions in the atmosphere limit the amount of vapor that can be discharged due to the environmental concerns that these emissions imply in terms of greenhouse effects. Therefore, the separation and recovery of the water contained in the waste gaseous streams, on one hand is a constrain to be addressed, on the other can represent a new source of water. Jointly with water consumption, power plants as well as fertilizer factories, cement and steel factories, chemical and petrochemical industries are the main sources of air pollution, forming harmful chemical compounds such as SOx, NOx, NH3, VOCs unburned hydrocarbons, and particulate matter. Membrane condenser is an innovative membrane operation that exploits the hydrophobic nature of microporous membranes to promote water vapor condensation and recovery. In addition, by opportunely tuning the operating conditions, it is possible to control the fraction of contaminants that can be retained in condensed water and, thus, the concentration of contaminants that can be emitted with the dehydrated gas stream. In this work, the we used a membrane condenser for water and contaminants recovery from synthetic streams (i.e., a saturated air stream with ammonia) simulating the plume of cooling tower or power plant. By modeling we predicted the process performance identifying the proper operating conditions for effectively recovering liquid water. In addition, the experiments performed adding NH3 or SOx in the feed stream showed the effectiveness of using this unit operation for contaminants control. The temperature difference between the membrane condenser and the plume resulted the most important parameter driving the concentration of the contaminant in the recovered liquid water. On the light of these results, membrane condenser is an interesting emerging technology for water recovery and as pre-treatment stage placed before other separation technologies, not only for membranes but also for other PSA, cryogenic, absorption, etc.