Superheated hydrolysis

Fats are hydrolysed to glycerol and fatty acids by boiling with acids and alkalis, by superheated steam and by the action of lipases. If alkalis are used for hydrolysis, the fatty acids combine with the alkalis to form soaps. Alkaline hydrolysis is therefore sometimes called saponification. 

Glycerol is obtained by the hydrolysis of fats and oils, and purified by distillation under reduced pressure with superheated steam. 

A two-step methanolysis-hydrolysis process37 has been developed which involves reaction of PET with superheated methanol vapors at 240-260°C and atmospheric pressure to produce dimethyl terephthalate, monomethyl terephthalate, ethylene glycol, and oligomeric products in the first step. The methanolysis products are fractionally distilled and the remaining residue (oligomers) is subjected to hydrolysis after being fed into the hydrolysis reactor operating at a temperature of ca. 270°C. The TPA precipitates from the aqueous phase while impurities are left behind in the mother liquor. Methanolysis-hydrolysis leads to decreases in the time required for the depolymerization process compared to neutral hydrolysis for example, a neutral hydrolysis process that requires 45 min to produce the monomers is reduced... 

Meluch et al.10 reported that high-pressure steam hydrolyzes flexible polyurethane foams rapidly at temperatures of 232-316°C. The diamines are distilled and extracted from the steam and the polyols are isolated from the hydrolysis residue. Good results were obtained by using reclaimed polyol in flexible-foam recipes at file 5% level. Mahoney et al.53 reported the reaction of polyurethane foams with superheated water at 200°C for 15 min to form toluene diamines and polypropylene oxide. Gerlock et al.54 studied the mechanism and kinetics of the reaction... 

An area of study related to this topic is the use of subcritical, but superheated water as a mobile phase for chromatographic separations [78], These separations use water heated to 100-220°C and pressures up to 50 bar, avoiding problems due to hydrolysis and oxidation, which is common when supercritical water is used. Although this is a new area of investigation, several reports on the hyphenation of HPLC using... 

Another concern for polystyrene- and some aromatic-based PEMs is hydrolysis of fhe sulfonic acid group from aromatic rings as well as hydrolytic cleavage of polymer backbone under fuel cell conditions for aromafic polymers including polyimides, poly(arylene ethers), poly(ether ketones), and poly(ether sulfones). It is well known that the sulfonation of aromafic rings is a reversible process especially at low pH and at elevated temperature (Scheme 3.3). The reversibility of sulfonation, for example, is used in fhe preparafion of trinitrotoluene or picric acid. Por the simplest membrane of the class of arylsulfonic acids (i.e., benzenesulfonic acid), fhe reacfion occurs upon freatment with a stream of superheated steam at 180°C.i ... 

Superheated and supercritical water are used in several applications. Supercritical water is most often used in the destruction of organic wastes, including some chemical warfare agents, as an alternative to incineration (Katritzky et al., 1996 Sherman et al., 1998). Recent reports describe the use of both forms as a solvent and as a reactant in synthetic chemistry (Katritzky et al., 1996 An et al., 1997). Some of the reactions investigated include metal-mediated alkyne cyclizations, Pd-catalyzed al-kene arylations, aldol reactions, the Fischer indole synthesis, and hydrolysis reactions. Waterborne coatings and the destruction of wastes in supercritical water are fully... 

Nitrothiophene is best prepared by hydrolysis of 4-nitro-2-thiophenesulfonyl chloride with superheated steam (equation 42). Nitration of 2-thiophenesulfonyl chloride gives a... 

The reaction of phosphorus with the alkalies is described under Phosphine. It is really a case of hydrolysis. This can also be effected by boiling water in the presence of certain metallic salts, which probably act by the intermediate formation of phosphides. Superheated steam at 238° to 260° C. and under a pressure of 57 to 360 atmospheres gives phosphine and orthophosphoric acid, thus —5... 

The principal advantages in the use of superheated water are that it is relatively easy to attain and the back-pressures required on the column are small. Thus even a modest length of narrow bore tubing can be employed to provide sufficient resistance to prevent boiling in the column and at these pressures many conventional spectroscopic flow cells can be used. Because of the high temperatures, there have been concerns about the thermal stability of the analytes, but of the numerous examples, there have been few reports of instability or a tendency for accelerated hydrolysis or oxidation, of the reported examples, only aspirin has hydrolyzed. Compounds which might be expected to be labile to oxidation or hydrolysis, such as the paraben antioxidants, have chromatographed without problems even up to 200°C [59]. 

The cooled fusion melt is leached with minimum amount of water to dissolve out the sodium cresolates and the resultant slurry is centrifuged to recover the sodium sulfite which is always associated with small quantities of sodium carbonate and sodium sulfate. Sodium carbonate is formed mainly by reaction between the molten alkali and atmospheric CO2. Sodium sulfate is produced from the sulfuric acids derived by hydrolysis of the sulfonic acids by the superheated steam produced during the reaction. 

Isomeric materials which have closely similar physical properties can be serious contaminants in hydrocarbons. With aromatic hydrocarbons, e.g. xylenes and alkyl benzenes, advantage is taken of differences in ease of sulfonation. If the required compound is sulfonated more readily, the sulfonic acid is isolated, crystallised (e.g. from water), and decomposed by passing superheated steam throu the flask containing the acid. The sulfonic acid undergoes hydrolysis, and the liberated hydrocarbon distils with the steam. It is separated from the distillate, dried. 

Mahoney et a/.87 have described the reaction of polyurethane foam and superheated water at 200 °C for 15 min, which leads to toluene diamines and polypropylene oxide. Hydrolysis of polyurethane and rubber mixtures has been used as a method not only of recovering valuable chemicals from the polyurethane fraction, but also to separate the polymers because rubber is inert to hydrolysis.89 The degradation takes place by contact with saturated steam at 200 °C for 12 h. This process may find particular applications in the treatment of rubber/polyurethane laminations. 

Acid hydrolysis by contact with superheated steam has been mainly applied... 

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