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Abstract

Methods are provided for recovering biuret from aqueous urea solutions and for producing relatively concentrated biuret-containing extracts which involve contacting a biuret-containing aqueous urea solution with the hydroxide ion form of an anion exchanger to retain at least a portion of the biuret on the exchanger, contacting the resulting biuret-containing ion exchanger with an aqueous extractant under conditions sufficient to form a biuret-containing extract, and contacting the resulting biuret-containing extract with the same or other biuret-containing anion exchanger in the same or subsequent cycles under conditions sufficient to increase the biuret concentration of the extract. The biuret-containing urea feed solution may also contain higher molecular weight urea condensation products, and the biuret can be selectively separated from such condensation products by the disclosed methods. Extracts containing about 1 weight percent biuret or more can be obtained from which biuret can be crystallized at temperatures above 0.degree. C., and purified biuret of as much as 99.9 percent plus purity can be obtained from solutions containing higher molecular weight urea condensation products such as triuret, melamine, ammelide, and/or others. An integrated process also is provided which involves heating urea at a temperature sufficient to form biuret (in the presence or absence of higher molecular weight urea condensation products) and recovering biuret from an aqueous solution of the resulting pyrolyzed urea as described.

First Claim