Water decarbonation

Air stripping is used to remove oxygen, carbon dioxide, ammonia and volatile organic compounds (VOCs) from water. Decarbonation removes alkalinity — carbonate, bicarbonate, carbon dioxide — by acidification and stripping the resulting carbon dioxide. Carbon dioxide is removed from RO product water to reduce the load on ion exchange resins downstream. Stripping of carbon dioxide increases the water pH, and thus reduces the corrosive properties of water. Forced air decarbonation is always used in conjunction with either RO or IX. 

Design Theory, Simplified Design Procedures, Column Diameter Selection, Water Deaeration, Water Decarbonation, Ammonia Stripping, Amine Regeneration, Hot Carbonate Regeneration, Side Strippers, Example Problem, Notation, References... 

While the ambient-temperature operation of membrane processes reduces scaling, membranes are much more susceptible not only to minute amounts of scaling or even dirt, but also to the presence of certain salts and other compounds that reduce their ability to separate salt from water. To reduce corrosion, scaling, and other problems, the water to be desalted is pretreated. The pretreatment consists of filtration, and may include removal of air (deaeration), removal of CO2 (decarbonation), and selective removal of scale-forming salts (softening). It also includes the addition of chemicals that allow operation without scale deposition, or which retard scale deposition or cause the precipitation of scale which does not adhere to soHd surfaces, and that prevent foam formation during the desalination process. 

Most processes will provide for degassing (decarbonation) by means of a degasser, which provides an up-current of air through a tower filled with polypropylene packing counterflow to meet a cascade of water saturated with carbon dioxide. The degassed water collects in a sump at the base of the tower. After degassing, the C02 content is normally less than 5 ppm. 

The anticancer agent Methotrexate (MTX) was conjugated with LDH by a coprecipitation method. To synthesize the MTX-LDH conjugate, powdered MTX was dissolved in decarbonated water, and titrated with NaOH (0.5 M) solution to give a 0.043 M solution of MTX at pH 7. The mixed metal solution of Mg(N03)2-6H20 and A1 (N03)3-9H20 with molar ratio Mg/Al = 2/1 was added to the MTX solution and the solution was titrated with NaOH solution until pH 9.5 to produce yellowish precipitates [7,26]. 

El Fil, H., Manzola, A. S. Benmor, M. 2003. Decarbonation of geothermal waters by seeding with aragonite crystals coupled with air bubbling. Applied Geochemistry, 18, 1137-1148. 

The design of the first commercial modules has allowed the commercial application of membrane contactors for some specific operations. This is the case of the Membrana-Charlotte Company (USA) that developed the LiquiCel modules, equipped with polypropylene hollow fibers, for the water deoxygenation for the semiconductor industry. LiquiCel modules have been also applied to the bubble-free carbonation of Pepsi, in the bottling plant of West Virginia [18], and to the concentrations of fruit and vegetable juices in an osmotic distillation pilot plant at Melbourne [19]. Other commercial applications of LiquiCel are the dissolved-gases removal from water, the decarbonation and nitrogenation in breweries, and the ammonia removal from wastewater [20]. 

A common problem with all the methods is that in preparations of LDHs with anions other than carbonate it is important to avoid contact with carbonate (e.g. from atmospheric carbon dioxide), since this anion is readily incorporated and tenaciously held in the interlayer. Consequently, decarbonated and deionized water is often used for such preparations and exposure of the reacting material to the atmosphere is kept to a minimum. 

In the metamorphic processes of dehydration and decarbonation of uniform thick sequences, filtration along the pressure gradient evidently played the main role in removal of water and carbon dioxide. Diffussion was of... 

The sequence of decarbonation processes is determined by the presence of iron oxides (hematite) and the water content of the fluids. In pure anhydrous siderite-chert rocks with an excess of quartz the following transformations... 

Malakhov, I. A., et al. (1995). Small-waste technology of water softening and decarbonization for heat network feeding. Teploenergetika, 12, 61-63. 

The controls on carbon dioxide would have been somewhat different. Today, carbon dioxide is stored in carbonate minerals in the ocean floor and on the continental shelf. Subduction, followed by volcanism, cycles the carbon dioxide to the mantle and then restores the CO2 to the air. Metamorphic decarbonation of the lower crust also returns carbon dioxide. The carbon dioxide is then cycled back to the water, some via rain, some dissolved via wave bubbles. Erosion provides calcium and magnesium, eventually to precipitate the carbonate. In the earliest Archean, parts of this cycle may have been inefficient. The continental supply of calcium may have been limited however, subseafloor hydrothermal systems would have been vigorous and abundant, exchanging sodium for calcium in spilitization reactions, and hence providing calcium for in situ precipitation in oceanic crust. 

A second place where membrane contactors are often used is before the electro deionization (EDI) step in UPW plants to remove residual CO2 gas. Removal of CO2 improves efficiency of EDI unit. Membrane contactors allow the opportunity to decarbonate water inline and under pressure just prior to EDI. 

The product water from a RO unit will have a low pH and most probably a high con-cenhation of carbon dioxide (15). The carbon dioxide can be removed and the pH of the product increased by use of a decarbonator. A decarbonator is a packed column in which product water is inhoduced at the top while either forced or induced air is introduced at the bottom. The air and water flow countercurrently over and around the column packing. The carbon dioxide is stripped from the water and exits from the decarbonator at the top in the air stream. 

The insoluble calcium carbonate (lime mud) is settled out from this mixture, filtered, and rinsed with water, which is then subsequently used for dissolving smelt. The supernatant liquor is now a solution of sodium hydroxide, sodium sulfide, and a small amount of unreacted sodium carbonate of nearly the correct composition required for a new batch of white liquor. Calcium carbonate in the lime mud is recycled by first calcining to decarbonate, followed by slaking to regenerate the calcium hydroxide required for a subsequent causticization (Eqs. 15.34 and 15.35). 

Aerosil 200 from Degussa and freshly decarbonated Ca(OH)2 were added to water (water solid = 50 1), and the dispersion was aged for 21 d. 

The host compound Mg/Al-LDH-[C1] was obtained by the hydrolysis of MgCL and Aids in weakly alkahne solutions (pH=9-10, NaOH) under nitrogen atmosphere at room temperature [17]. All water was deionized before use and was decarbonated by boding for at least two hours. The LDH was... 

M Zn(N03)2.6H20 solution During the procedure, pH is kept at 6 with NaOH. After addition of the solution, the solution is refluxed for one week under nitrogen atmosphere. The solid is then obtained by centrifugation and washed with water, followed by lyofilization. Water used in this procedure must be decarbonated. 

Hydrotalcite-like compounds (HTlcs) have attracted much attention in recent years as catalyst precursors and catalyst support. This is due to (i) their ability to accommodate a large variety of bivalent and trivalent cations (ii) the homogeneous mixture of the cations on an atomic scale and (iii) the formation of thermostable mixed oxides, often denoted as ex-HTlcs, with high surface area upon decomposition. The first two properties are a result of the precursor while the last property appears to be related to the decomposition mechanism. The transitions in the structural properties of Co-based hydrotalcites upon high temperature treatments have been extensively studied in our group.15,16 In the first decomposition step, water is removed from the structure. This transition is followed by dehy-droxylation and decarbonation, as well as carbonate reorganization in the interlayer. Thermal treatment in air finally leads to a solid solution of cobalt spinels (Co(Co, A1)2C>4). Mixtures of CoO and C0AI2O4 are formed upon treatment in inert. 

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