GB778739A - Process for the production of trisodium pyrophosphate hydrates - Google Patents

Abstract

Trisodium pyrophosphate hydrate is produced by intimately mixing a mixture of disodium dihydrogen pyrophosphate and tetra-sodium pyrophosphate with an amount of water sufficient to form a hydrate but insufficient to dissolve the product. When stoichiometric proportions of the disodium dihydrogen phosphate and tetrasodium pyrophosphat are not employed the trisodium pyrophosphate hydrate may contain small amounts of di- and tetra-sodium pyrophosphate. The water may be incorporated in the pyrophosphate mixture by spraying a mixture of di- and tetra-sodium pyrophosphates as it is tumbled in a rotating drum. Alternatively the hydration can be combined with a grinding operation whereby the pyrophosphate mixture is worked in a ball mill and a mist of water applied thereto. The disodium-tetrasodium pyrophosphate mixture can be produced directly by transforming a sodium ortho phosphate calcinate, which consists of an intimate mixture of anhydrous mono- and di-sodium ortho phosphate and has a Na2O : P2O5 ratio of 1.5:1, into pyrophosphate by heating to temperatures between 200 and 260 DEG C. The calcinate is produced by completely dehydrating a mixture of mono- and di-sodium orthophosphate hydrates at temperatures below 200 DEG C. The pyrophosphate mixture obtained by heating the calcinate may be transformed directly into trisodium pyrophosphate hydrate, but if a higher temperature, for example 290 DEG C. is chosen for the conversion of the orthophosphate to pyrophosphate, sodium tripolyphosphate is simultaneously formed particularly if the Na2O : P2O5 ratio is increased; on hydration a mixture of trisodium pyrophosphate hydrate and sodium tripolyphosphate hydrate is obtained; such a mixture may be used for meat-tenderizing and as a fat emulsifier. According to examples (1) a mixture of disodium dihydrogen pyrophosphate and tetrasodium pyrophosphate in a molar ratio of 1:1, are introduced into a stainless steel rotary drum fitted with lifters and which rotates at 10 revolutions per minute 8 mols of water are sprayed on to the tumbled material and the mixture is then dried in a hot air drier at 80 to 90 DEG C. to a water content of 6.1 per cent. A further example relates to hydration with 3 mols of water. Crystographic data of the trisodium pyrophosphate monohydrate is provided.