US 4,877,594 A · Purification of phosphoric acid

Abstract

A mixture of hydrophobic and hydrophilic extractants is used to separate phosphate values from impurities found in phosphoric acid. In one approach, impurities are removed from phosphoric acid and the phosphate values are recovered, by introducing polyphosphates and ammonium ions into the impure acid, and contacting the impure acid with a mixture of low and high molecular weight alcohols, one of which is hydrophilic and the other hydrophobic, in a single stage. The phosphate values segregate to the high molecular weight alcohol fraction, and the impurities segregate to the low molecular weight alcohol fraction. After separation of the alcohol solutions, the phosphate values and the impurities are separated from their respective extractant solutions, and the alcohols recirculated. Polyphosphates and ammonia are preferably provided by reacting a portion of the original feed acid with ammonia at elevated temperature in a pipe reactor.

Claims19

Dependent claims

A process for purifying impure phosphoric acid, comprising the steps of:

furnishing impure phosphoric acid;
adding to the impure phosphoric acid, to form a modified acid, a modifier selected from the group consisting of
a polyphosphate, and
a cation selected from the group consisting of ammonium ion and an alkali metal ion;
mixing the modified acid with a mixture of alcohols, the mixture of alcohols including both
a low molecular weight alcohol selected from the group of alcohols having from 1 to 3 carbon atoms, and mixtures thereof, and
a high molecular weight alcohol selected from the group of alcohols having from 4 to 12 carbon atoms, and mixtures thereof;
and
separating the mixture of alcohols and prepared acid into two fractions, a first fraction including the high molecular weight alcohol and the phosphate values dissolved therein, and a second fraction including the low molecular weight alcohol and the impurities originally present in the impure phosphoric acid.

6 more elements

A process for purifying impure phosphoric acid, comprising the steps of:

furnishing impure phosphoric acid having from about 52 to about 72 percent by weight phosphate;
diverting from about 5 to about 25 percent of the impure acid to a pipe reactor wherein the acid is heated and ammonia is added to the heated acid, whereby the orthophosphates in the acid are converted to polyphosphates, thereby forming a polyphosphate melt;
introducing the polyphosphate melt into the impure acid;
mixing the prepared acid with a mixture of alcohols, the mixture of alcohols including both
a low molecular weight alcohol selected from the group of alcohols having from 1 to 3 carbon atoms, and mixtures thereof, and
a high molecular weight alcohol selected from the group of alcohols having from 4 to 12 carbon atoms, and mixtures thereof;
separating the mixture of alcohols and prepared acid into two fractions, a first fraction including the high molecular weight alcohol and the phosphate values dissolved therein, and a second fraction including at least some of the low molecular weight alcohol and the impurities originally present in the impure phosphoric acid;
separating the phosphate values from the high molecular weight alcohol of the first fraction;
recycling the separated high molecular weight alcohol to the step of mixing;
separating the impurities from the low molecular weight alcohol of the second fraction;
and
recycling the separated low molecular weight alcohol to the step of mixing.

9 more elements

Dependencies are inferred from the claim text.

Purification of phosphoric acid

Life of this patent

Purification of phosphoric acid

Life of this patent

Abstract

Claims19