Moisture residual

In some cases the chemical method given by Karl-Fischer titration can also be applied for residual water determination. This method is based on oxidizing methyl sulfite with iodine into colorless iodide and methyl sulfate. The reaction only takes place when free water is available in the system. 

Additional, recently developed methods for the determination of residual water content are the near infrared (NIR) absoption method and nuclear magnetic resonance (NMR). The NMR method has been successfidly used for the quick determination of residual water with high spatial and temporal resolution in bulk materials such as granules, applying a magnetic field gradient approach (Bliimich, 2005). 

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Many materials need to be dried prior to their analysis to remove residual moisture. Depending on the material, heating to a temperature of 110-140 °C is usually sufficient. Other materials need to be heated to much higher temperatures to initiate thermal decomposition. Both processes can be accomplished using a laboratory oven capable of providing the required temperature. 

Each food or food ingredient shows a characteristic equiHbrium relative humidity at a given moisture content and temperature. Thus as a food is dried and its moisture content is reduced from its fresh value where water activity is generally 1.0, to lower and lower values, the equiHbrium water activity of the food decreases as a complex function of residual moisture. The shape of the equiHbrium relative humidity—moisture content curve is set by the chemistry of the food. Foods high ia fmctose, for example, biad water and thus show lower water activities at high moisture contents. Dried pmnes and raisias are examples. Drying can be terminated at any desired moisture content and hence any water activity. 

The burning of the ligneous portion of the black Hquor produces sufficient heat in the furnace to sustain flash drying of residual moisture, salt-cake reduction, and chemical smelting. The heat in the gas passing through the furnace, boiler, and economi2er produces steam for power and process. 

The quantity of undrainable residual moisture caimot be predicted without the benefit of experimental data. Equation 17 (6) indicates the important parameters where the exponents were determined using limited experimentation. Introducing the approximation that is proportional to 1/d, where s is the specific surface area per weight of solid, the modified equation for undrainable liquid becomes... 

Glass-Transition Temperature. The T of PVP is sensitive to residual moisture (75) and unreacted monomer. It is even sensitive to how the polymer was prepared, suggesting that MWD, branching, and cross-linking may play a part (76). Polymers presumably with the same molecular weight prepared by bulk polymerization exhibit lower T s compared to samples prepared by aqueous solution polymerization, lending credence to an example, in this case, of branching caused by chain-transfer to monomer. 

Evaporation. Evaporation can be used to separate volatile compounds from nonvolatile components and often is used to remove residual moisture or solvents from soHds or semisoHds. Thin-film evaporators and dryers are examples of evaporation equipment used for this type of appHcation. Some evaporators are also appropriate for aqueous solutions. 

Carbon dioxide is ordinarily dehydrated duriag the Hquefactioa cycle to preveat free2e-ups ia the coadeaser and flow valves ia the Hquid lines. Ia some cases brittie or cmmbly blocks of dry ice have beea formed. This difficulty has beea overcome either by varyiag the residual moisture coateat of the Hquid carboa dioxide, or by injecting minute quantities of colorless mineral oil or diethylene glycol iato the Hquid carboa dioxide entering the press. If the dry ice is to be used for edible purposes, the additive must meet FDA specificatioas. 

Although all the techniques are effective, in industrial appHcations there is rarely time to achieve an equiHbrium reduced saturation state (see Filtration), so variables that affect only the kinetics of dewatering and not the equiHbrium and residual moisture are also very important. The most important kinetic variables in displacing the Hquid from the soHd are increases in pressure differentials and viscosity reduction. 

Use of Surfa.cta.nts, Although the use of steam to improve dewatering is consistently beneficial, the effects of surfactants on residual moisture are highly inconsistent. Additions of anionic, nonionic, or sometimes cationic surfactants of a few hundredths weight percent of the slurry, 0.02—0.5 kg/1 of soHds (50), are as effective as viscosity reduction in removing water from a number of filter cakes, including froth-floated coal, metal sulfide concentrates, and fine iron ores (Table 2). A few studies have used both steam and a surfactant on coal and iron ore and found that the effects are additive, giving twice the moisture reduction of either treatment alone (44—46,49). 

Table 2. Effect of Surfactants on Residual Moisture in Filter Cakes...

Fig. 8. Drying time and rate profiles for leather pasted on glass plates and dried in two temperature stages. Gas velocity = 5 m/s in parallel flow, 71°C in the first stage, 57°C in the second. The falling rate, drying rate is proportional to residual moisture content.

Where applicable, dry steam is passed through the dehquored cake to raise the temperature of the residual moisture, reduce its viscosity, and lower its content. The final diying or cooling period which follows steam filtration uses the residual heat left in the cake to evaporate some additional moisture. 

Formaldehyde emission from finished panels is due to the residual formaldehyde present as a gas in the wood and recesses of UF-bonded and MUF-bonded boards as well as dissolved in the boards residual moisture content. On the other... 

Similarly, a variety of drier types are available to remove residual moisture eontent for whieh tests are normally required prior to final equipment seleetion. In eaeh of these operations, eare should be taken to aseertain the extent of partiele size ehange due to attrition and fragmentation, or, in some eases, granulation within the downstream units. 

A second variable is the amount of residual moisture present in the extremely hygroscopic potassium fluonde Solvents are often used to remove this moisture hy azeotropic distillation When the reaction mass is anhydrous, the solvent is... 

No mechanism for cracking in N2O4 has been established . In organic media crack velocities are similar to those obtained in distilled water. Lowering the water content results in lower velocities. Not all authors attribute failures in organic liquids to the residual moisture . Furthermore, part of the fracture may be transgranular . Water additions to methanol increase crack velocities as do halide additions. In oils velocities are similar to those in organic liquids and distilled water. 

The quantitative analysis procedure involves benz extr of TNT, water extr of AN, and taking of the A1 content as insol residue. Moisture content is detd by the Karl Fischer method described in ASTM Method E203-62, except that 8 to lOg samples are added to methanol. Specific gravity is detd by water displacement, and workmanship by visual examination... 

The wet steam passes through steam-water separators within the top drum. Separated water is returned to the inlet of the external downcomer, while the moist-to-dry steam may pass through a secondary steam-water separator to remove any residual moisture before passing into the steam header part of the steam delivery system. 

The physical forms indicated are those which, for each specific type of product, assure product flowability within the reported range of residual moisture they can be achieved by specific mechanical devices operating at the outlet of the evaporator and cooler. 

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