Solubility Equilibria of Sodium Sulfate at Temperatures from 150 to 350°.¹ III. Effect of Sodium Hydroxide and Sodium Phosphate

Abstract

The present paper is the third in a series presenting the results of an investigation carried out in coiiperation with the Joint Research Committee on Boiler Feedwater Studies dealing with the solubility of sodium sulfate in various solutions in the temperature range from 150 to 350". The first paper5 gave solubility data for sodium SUIfate, in sodium hydroxide-sodium chloride solutions, and the secondfi for sodium sulfate in SOdium hydroxide-sodium carbonate solutions. This paper presents data for (1) a design for a new high temperature solubility bomb, ( 2 ) the solubility of trisodium phosphate in water and in sodium hydroxide solutions, (3) data for the system sodium sulfate-trisodium phosphate-water, (4) the solid phases in this system, and (5) the effect of sodium hydroxide on the system. These studies involving the phosphate are the most complicated, and perhaps the most interesting, of the three solubility investigations. High Temperature Solubility BombThe bomb originally used in the study of the high temperature solubility equilibria of sodium sulfate has been described in the first paper5 of this series. As the investigation proceeded several disadvantageous features were found in this equipment. It has been redesigned and the difficulties have been corrected in the bomb shown in Fig. 1. The body is open a t both ends to make for easy machining] with the sampler as well as the bottom held in place by studs. The necessary seals are formed by metal-to-metal contact between seats machined a t 60" so that no gaskets or material other than the bomb metal comes in contact with the solution. The valve (I) Published by permission of the Director, U. S. Bureau of Mines. (Not subject to copyright.) (2) Research chemical engineer, Joint Research Committee on Boiler Feed-Water Studies, attached to Eastern Experiment Station, stem is large enough to eliminate sticking and danger of twisting off. SQUARE FOR WRENCH ~ PACKING Fig. l.-Solubility bomb (dimensions in inches) : firessure, 200 atmospheres or 3000 lb. per sq. in.; volume, L U L~I W I L U saiiryicr 111 p a c e YJU CC., UCIUW aamyirr IYW CF., above sampler 110 cc., sampler 18 cc.The sampler is enclosed in the bomb to ensure sampling a t the operating temperature, and the end may be equipped with a filter of carbon or 843-849 (1936) ' fine wire screen if this is desirable. Crane pack-

Two-liquid-phase boundaries and critical phenomena at 275-400.degree.C; for high-temperature aqueous potassium phosphate and sodium phosphate solutions. Potential applications for steam generators

“…A two-liquid-phase region was also discovered but with a minimum temperature of 360 °C, which was approximately 85 °C higher than that estimated for corresponding Na2HPC4 solutions (2). Substitution of potassium phosphate for sodium phosphate as an additive would therefore prevent the formation of a second liquid phase in the region of steam generator operation (275-325 °C) that otherwise could have caused thinning as proposed by Garnsey (7). This substitution might again make phosphates useful in eliminating particular problems of corrosion (including denting) as suggested earlier (3).…”

“…After the discovery by Broadbent et al {2) that aqueous solutions of disodium hydrogen phosphate form two immiscible liquids at temperatures near 300 °C, Garnsey (7) proposed that the resulting concentrated and strongly corrosive solution, possibly produced by boiling concentration, may have corroded the steam generator tubes to cause thinning. Recently, the 0021-9568/82/1727-0175501.25/0 analogous dipotassium hydrogen phosphate-water system has been studied at this laboratory at temperatures from 100 to 400 °C (3), motivated by the earlier work of Broadbent et al (2), by the proposals of Garnsey (7), and by knowledge that at temperatures below 100 °C potassium salts are more soluble than the analogous sodium salts (4,5). This recent work showed that aqueous K2HPC4 solutions at high temperatures still were much more soluble than those of Na2HP04.…”

The Chemistry of Sodium Phosphates.

“…E. OPTICAL DATA 1. Properties of pure compounds Ingerson and Morey (60) have recently collected all available optical data on sodium phosphates (8,12,28,65,95,114) and added a few of their own. Their 10 Suggested to the writer by Dr. A. S. Richardson during the course of our studies.…”

Evaluation and correlation of steam solubility data for salts and minerals of interest in the power industry

“…The highest temperature at which there are measurements for liquid-phase solubility is 350 °C. The mole-fraction solubihty at that temperature is 1.65 x 10^a ccording to Schroeder et al [28] and 5.97 x 10^a ccording to Wetton [27]. We decided to give more weight to the more recent study [27], since the complex chemistry was not appreciated at the time of the Schroeder et al [28] work.…”

“…The mole-fraction solubihty at that temperature is 1.65 x 10^a ccording to Schroeder et al [28] and 5.97 x 10^a ccording to Wetton [27]. We decided to give more weight to the more recent study [27], since the complex chemistry was not appreciated at the time of the Schroeder et al [28] work. We therefore used a value of 5.0 x 10^. For the distribution between vapor and liquid, we used the data of Goodstine [29, supplemented by additional data courtesy of ABB Combustion Engineering], who measured the partitioning of sodium between vapor and liquid phases at various concentrations and pressures.…”