Acid loss evaporation

Technetiiun can also be isolated quantitatively from molybdate using Dowex-1 resin in the chloride form . Molybdate can be eluted with 0.1 M hydrochloride acid pertechnetate, however, is firmly adsorbed under these conditions. It can be readily eluted with 4.0 M nitric acid. The only drawback of this separation is the need to recover technetium from nitric acid solution. If the acid is evaporated with great care, losses may be kept quite low. 

By this method of extracting the esters from their hydrochlorides, neither that of tyrosine, which remains behind combined with alkali, nor those of the diamino acids, which are soluble with difficulty in ether, are obtained. This is advantageous for the subsequent process of separation, but the method has the disadvantage that the whole quantity of esters is not taken up by the ether on account of their destruction by the alkali. In order to avoid their loss, the mass of carbonate is treated with excess of hydrochloric acid and evaporated down, the potassium... 

The product, if pure, will give little or no precipitate when boiled with a little dilute acetic acid. Losses incurred during recrystallization may be minimized by evaporating... 

J. J. Berzelius found that some acid is volatilized when phosphoric acid is heated in an open crucible, but not in a covered crucible, and H. Rose showed that in an open vessel all the phosphoric acid can be volatilized. J. B. Bunce said that some acid is volatilized with the steam, but G. C. Wittstein, and 0. R. Fresenius showed that this is not the case when phosphoric acid is evaporated in an open dish, although some of the evaporating liquor may be carried away mechanically if the ebullition is rapid. E. Lautemann, S. Leavitt and J. A. Leclerc, and G. Lechartier have studied the loss of phosphoric oxide during the calcination of ash—about 2-14 per cent, was lost at low redness, 2-08 at bright redness. According to R. Bunsen, phosphoric acid is 23 times more volatile than sodium carbonate. 

Transfer the filter paper and precipitate into a tared platinum crucible, char, and ignite at 900° to constant weight. Moisten the residue with a few drops of water, add 15 mL of hydrofluoric acid and 8 drops of sulfuric acid, and heat on a hot plate in a hood until white fumes of sulfur trioxide evolve. Cool add 5 mL of water, 10 mL of hydrofluoric acid, and 3 drops of sulfuric acid and evaporate to dryness on the hot plate. Heat cautiously over an open flame until sulfur trioxide fumes cease to evolve, and ignite at 900° to constant weight. The weight loss after the addition of hydrofluoric acid represents the weight of Si02 in the sample taken. 

The processing of milk into various dairy products may result in vitamin C losses. Ice cream contains no vitamin C, nor does cheese. The production of powdered milk involves a 20 to 30 percent loss, evaporated milk a 50 to 90 percent loss. Bullock et al. (1968) studied the stability of added vitamin C in evaporated milk and found that adding 266 mg of sodium ascorbate per kg was sufficient to ensure the presence of at least 140 mg/L of ascorbic acid during 12 months of storage at 21 °C. Data on the stability of vitamin C in fortified foods have been assembled by deRitter (1976) (Table 9-15). 

Oxygen and Ascorbic Acid Loss in TASTE Evaporators... 

The proper temperatures for the pasteurization of vinegar range from 140° to 160° F. Experience has shown that if properly carried out a temperature of 140° F. is effectual for this purpose, but it is the minimum—no lower temperature can be depended upon to produce the desired result On the other hand, a temperature of 160° F. should not be exceeded, for the reason that it is not required and may cause an unnecessary loss of acetic acid by evaporation. 

It should be pointed out that although //is not consumed by the reaction, its value is not locally constant because diffusion during PEB and evaporation (as well as unwanted side reactions involving the acid, i.e., all acid loss mechanisms) may induce local variations in the concentration of H. This condition necessitates the use of reaction-diffusion equations to accurately model this system. However, the assumption that H is constant is not without merit, for it is valid under certain conditions. Besides, it helps to simplify the problem. 

Another mechanism for acid loss occurring during PEB is evaporation from the top of the resist. The amount of evaporation depends on the size of the acid and the degree of its interaction with the resist polymer. A small acid such as trifluoroacetic acid may have appreciable evaporation during PEB. The evaporation rate is expressed as... 

Because of the great solubility of HIO3, large losses occur during crystallization therefore, aqueous HIO3 solutions may be mixed with an equal volume of concentrated nitric acid and evaporated to one third their volume. This usually results in separation of HIO3 even from hot solutions. 

A 2.134-g. (0.0202-mol) quantity of palladium metal is dissolved in aqua regia (3 ml. of 15 N HNOj + 12 ml. of 12 N HCl) which has been allowed to stand for about 30 minutes. If powdered palladium is used, no heat is required to effect solution for other forms of palladium metal, some heating is usually required. The solution is evaporated on a steam bath to a brown-black syrup, which is then covered with 5 ml. of 12 N hydrochloric acid and evaporated to moist salts. This treatment with hydrochloric acid is repeated twice more to remove nitric acid and to destroy nitrosyl complexes. The resulting tetrachloro-palladic(II) acid is dissolved, with stirring and heating, in a minimum volume of water (approximately 100 ml.), and 4.0 g. (0.068 mol) of sodium chloride is added. The dark brown solution is concentrated to one-half its volume on a hot plate and is then evaporated to dryness on a steam bath. This evaporation removes excess hydrochloric acid, which if allowed to remain leads to contamination of the tetra-amminepalladium(II) tetrachloropalladate(II) with the isomeric hydrochloric acid also prevents loss of product owing to... 

The sulphate content of wet acid is generally 2-5% and phosphoric acid losses in the precipitated calcium sulphate (phosphogypsum) are sometimes 3-10%. Most of the fluorine is evolved from the process in gaseous form during acidulation of the rock and consequent evaporation, but some remains in the calcium sulphate and the acid product. Up to 50% of the Cd impurity originally present in the ore is believed to be removed by the calcium sulphate. 

Sorbic acid has to be dissolved in boiling water due to slow dissolution in cold water. But because sorbic acid is volatile with water vapour, loss of sorbic acid has to be prevented by immediately closing the vessel after the additimi of the boiling water. When the preparation is processed in a Stephan mixer in vacuum the sorbic acid may evaporate fast as well. An alternative is to use potassium sorbate instead of sorbic acid and to adjust the pH of the preparation subsequently. 

The suppression of acid loss can be a more challenging problem for improving the durability of HT-PEMFC MEA. The acid loss is caused by evaporation, compression pressure of stack, diffusion from MEA to flow field, and volume change caused by hydration of acid which can occur when exposed to highly humid environment. The retention of acid within the catalyst layer can be improved by adding materials that can either absorb acid [40] or form... 

The usual method applied for the acid leaching evaluation is to analyze the anodic and cathodic off-gasses for traces of vaporized acid. This is typically done by collecting the acid in water bubbler flasks. However, this does not necessarily provide a realistic picture of the severity, since only a single mechanism for the proposed acid loss is considered, i.e., the evaporation. Furthermore, it is apparent that not all of the escaped acid in the gas phase is carried all the way out with the fuel cell exhaust due to recondensation before collection. This conjecture is based on... 

Acid evaporation measurements Acid losses [pg/(m s)] References... 

Acid transfer within the MEAs and its loss out of the cell are of critical concern. Via an evaporation mechanism the acid loss seems to be at a level of up to a few pg/(m s) of the electrode area. Acid transfer within the MEAs, not necessarily resulting in acid loss out of a cell, seems more critical for the fuel cell performance degradation. 

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