Salt solubility in the system KHCO3-(C2H5)2NH2Cl-H2O at 30°C

Abstract

2 О, which is the diagonal cross section of the quaternary mutual system K + ,(С 2 Н 5 ) 2 N ||НС Cl --Н 2 О along the stable pair of salts, are responsible for the physicochemical trends of formation of KHCO 3 in the crystalline state from KCl, diethylamine, and CO 2 . The solubility of the salts in the system has been studied most thor oughly only at 10°C and at a standard temperature of 25°С [1]. Some segments of the 20°С solubility iso therm in the phase diagram have been presented in [2,3]. Since the phase equilibria in this water-salt system are essentially a laboratory model of the synthesis of KНСО 3 from various real solutions at different tem peratures, we found it interesting to study the solubil ity of these salts at 30°С. EXPERIMENTALSalt solubility was studied by a preparative method at 30 ± 0.1°С in a temperature controlled water jack eted vessel. The composition of the equilibrium solid phase was determined by a modified "wet residue" method [4-6] with allowance that the initial reaction mixture and the wet residue are on the tie line con necting the crystallizing phase and the saturated solu tion.Because potassium and diethylammonium bicar bonates undergo partial decarboxylation during satu ration, the vessel for solubility experiments was con stantly fed with gaseous CO 2 to reduce their decarbox ylation.An initial weighed sample was placed in a vessel equipped with a temperature controlled jacket, a mechanical stirrer, and an inlet for CO 2 bubbling.For the equilibrium in the system to be established as soon as possible (2-3 h), the components of the ini tial reaction mixture produced by the reaction and one of the starting compounds were mixed in a certain order. First the most poorly soluble component (KHCO 3 ) was added to water and stirred under tem perature control for 3-5 min. Then the more soluble salt (KCl) or diethylamine was added and the system was again kept under temperature control for 3-5 min. Finally, the most soluble salt (diethylammonium chlo ride) was added and the temperature control was con tinued until equilibrium was established in the system. The required amount of diethylamine was successively added in ten equal portions every five minutes.Establishment of the equilibrium was detected by measuring the refractive index of the solution on an RL1 refractometer every 20 min. The first measure ment was performed 40 min after the start of the experiment. The equilibrium was believed to be estab lished if three successive refractive indices differed by at most 0.0005. After the equilibrium was established (4 h), the stirring was stopped and the solution was allowed clarify. The liquid phase was sampled for anal ysis in volumetric flasks with distilled water.In the study of the water-salt system, we designed the experiment with the aim of minimizing the time cost required to determine the compositions of eutonic solutions and univariant equilibrium lines [5].The composition of the liquid phase was deter mined analytically [7,8]. The content of the chloride ions was determined b...