Removing salt by ethanol precipitatation and nanofiltration to preparation gluconic acid

Two desalination methods were compared in preparation of gluconate. Ethanol precipitation and nanofiltration were respectively investigated to remove sodium chloride in the reaction mixture of sodium gluconate and hydrochloric acid. The optimal technology of ethanol precipitation was obtained by the orthogonal test. Effects of sodium gluconate to hydrochloric acid ratio,volume fraction of ethanol and incubation time on the yield of gluconic acid and desalinization ratio were investigated under single factor test. The results showed that it yielded 61.09% of gluconic acid and removed 80.44% of salt under the following optimal condition:one part of sodium gluconate was reacted with 2 volume of HCl(in equimolar ratio),and then ethanol was added to 75%(final concentration) and incubated at room temperature for 24 h. The optimal nanofiltration(150 D molecular cut-off) technology was:10.0 L solution was nanofiltrated at 0.3 MPa and 30 ℃ for 110 min.Under this condition,85.99% of gluconic acid was recovered,10.01 L/m2 h of membrane flux was produced and78.66% of salt was removed after nanofiltrated for four rounds. Two methods of desalination had high desalination rate,nanofiltration was better than ethanol precipitation.