Prospects for the use of liquid waste from the production of sodium carbonate as a coolant based on the ternary system CaCl2-K2Cr2O7-H2O

Abstract

Currently, the urgent problem is the secondary use of distillation liquid - a waste product from the production of sodium carbonate, which is an aqueous solution containing about 10 % calcium chloride and a small amount of other salts. It is proposed to use a solution based on a distiller liquid as a coolant in a heat exchange system in the production of soda. The introduction of potassium dichromate into the system creates an inhibitory effect and prevents pipe corrosion. To study phase equilibria in the CaCl2 - K2Cr2O7 - H2O system, state diagrams were constructed at temperatures of 20, 3, and -7°C. With decreasing temperature, the homogeneous region noticeably decreases and shifts to the CaCl2 - H2O axis. The eutectic point is limited to a very narrow area in which the weight fraction of potassium dichromate does not exceed 3%.Using the Skrynemakers method, it was found that in a region with a calcium chloride content of less than 40 %, potassium dichromate crystallizes. For the region adjacent to the apex of calcium chloride, it is impossible to establish the composition of the solid phase and the boundaries of its crystallization using the Skrynemakers method. This is due to the fact that the binary system CaCl2 - K2Cr2O7 is a ternary reciprocal system K +, Ca2 + Cl-, Cr2O72- . In this area, the formation of solid solutions or compounds based on the binary system K2Cr2O7 - CaCr2O7 is supposed. For the temperature range from -7 ?С to 50 ?С, the refrigerant composition was proposed: 3 % K2Cr2O7 - 10.2 % CaCl2 - 86.8 % H2O. In the temperature range from 20 ?С to 60 ?С, the composition of the solution is: 6 % K2Cr2O7 – 10 % CaCl2 – 84 % H2O.