Transport Characteristics of Neutralization Dialysis and Desalination of Tap Water

Abstract

In neutralization dialysis, the salt solution is desalinated continuously. The cations in desalination compartment are exchanged with protons in the acid compartment across a cation-exchange membrane and the anions are exchanged with hydroxide ions in the base compartment across an anion-exchange membrane. A simple index (C/1), where C is the source phase concentration (mol cm-3) and J is the flux (mol cm-2 min-I), was proposed for the estimation of the desalination properties in neutralization dialysis. The index was based on the concepts of the ion-exchange reaction rate at the membrane interface and was related to the permeation constant in the source-phase boundary layer at the membrane interface, P a (cm min-I), as CIl = lI(k,·C ex ) + lIP a , where k l is the rate constant of ion-exchange reaction (mol-I cm 4 min-I) and C ex is the ion exchange capacity of the membrane (mol cm-3 ). The desalination efficiency increased with the decrease of the desalination compartment thickness and the decrease of the linear velocity, which can be estimated well by using the index. Tap water was desalinated by neutralization dialysis and pure water was obtained at the outlet of the desalination cell.Neutralization dialysis is a continuous desalination method first reported in 1986,1.2 which uses ion-exchange membranes and is based on Donnan Dialysis. for the separation of non-electrolytes of organic solutes from ions.' It is also efficient to remove weak acids and bases such as silicate ions, 7 and the potential of this method to be used in the food industry has been reported. 10.1 I This method can be also used in the water purification. 7 The feed solution was circulated in our previous works,I.2.7 but the purified water is better obtained just after the outlet of the cell without circulation for desalination.In this paper, we tried the desalination experiment without circulation of the feed solution. We will propose at first a simple index (C/J), where C is the source phase concentration (mol cm-3 ) and J is the flux (mol cm-2 min-I), to estimate the desalination properties in neutralization dialysis. In the derivation of the index, we do not depend on the concepts of the conventional quasi-equilibrium but on the ion-exchange reaction rate at the membrane interface J2 to interpret the transport phenomena accurately. Next, we will discuss the desalination properties of the neutralization dialysis by using this index. Finally, we will report the result of the tap water desalination by neutralization dialysis. ExperimentalApparatus. Neutralization dialysis was carried out in the cell shown in Fig. 2. The feed solution, the acid solution, and the base solution were circulated in the previous research,7 but in this paper, the feed solution was not circulated, although the acid and the base solutions were circulated at a rate of 100 cm 3 min -I. The solutions were pumped from the reservoirs with tubing pumps and the feed solution was collected for analysis just after the outlet of the desalination cell. The compartments in th...

Hydrogen Ion (H+) in Waste Acid as a Driver for Environmentally Sustainable Processes: Opportunities and Challenges

“…Note that KCl in the middle chamber is near-completely desalinated. Deionization of tap water with low total dissolved solids has been achieved in the laboratory using pure acid and base , but the process is economically unsustainable for brackish and seawater desalination due to the large requirement of pure mineral acids and neutralizing bases. Figure C presents the results obtained by German for brackish water desalination using a biorenewable organic acid, namely, citric acid; again, high percentage desalination of NaCl (i.e., reduction from 5000 mg/L NaCl to less than 1000 mg/L) is achieved in 70 h. In this experiment, sodium carbonate was used as a neutralizing base, implying magnesium carbonate, an abundant and inexpensive base, may also be quite suitable.…”

Neutralization Dialysis for Phenylalanine and Mineral Salt Separation. Simple Theory and Experiment

“…Neutralization dialysis (ND) was proposed first by Igawa [24] and has demonstrated a higher efficiency than DD for desalination of multicomponent solutions [25,26], separation of electrolytes (substances that are present in solution in the form of ions and can be transported through IEM) [24], the extraction of weak inorganic electrolytes [27] or carboxylic acids [28], as well as the selective fractionation of various amino acids [29,30] (the substances that participates in protolysis reactions) or mixtures of mineral salt and amino acid. In recent years, new modifications of ND have appeared, for example, capacitive neutralization dialysis, which is used to generate electricity by utilizing acidic and alkaline wastewater using ND techniques in combination with capacitive deionization [31,32].…”

“…The protons and hydroxyl ions in the desalination compartment react with each other to form water. It has been established that the efficiency of ND demineralization increases with a decrease in the intermembrane distance in the desalination compartment as well as with a decrease in the solution flow rate in the case of the direct-flow hydraulic mode [25]. If a batch hydraulic mode is used, on the contrary, it is necessary to increase the solution flow rate in order to reduce the diffusion boundary layer (DBL) thickness near the membrane surface [33,34].…”

Selective Separation of Organic Electrolytes by Neutralization Dialysis with Grafted Polyethylene Films

“…A variety of synthesized polymer membranes are involved in membrane-separation processes, such as energy saving, resources recovery [1], and environmental preservation mainly for removal of metal or inorganic ions such as K + , Ca 2+ , Mg 2+ , NO 3 , and SO4 2 [2][3][4] and organic electrolytes [5][6][7][8] and for desalination [9][10][11][12]. Most of these membranes are highly crosslinked in order to increase their mechanical stability and avoid excessive water swelling.…”