Experimental Study on Molten Salt Oxidation of High Salt Content Pharmaceutical Residue

Abstract

The pharmaceutical residues from chemical synthesis pharmaceutical industry often contain some alkali salts due to the widely use of alkali salts in the manufacturing process, the waste management of such is a significant challenge. Generally, the residues are disposed by landfill and incineration. However landfill is unsustainable and the incineration's efficiency is effected by furnace slag-bonding during combustion, that affects the widely use of incineration. On the other hand, molten salt oxidation is an efficient, flameless thermal process, has the inherent capability of destroying organic constituents of wastes while retaining the inorganic constituents in the molten salt. Therefore, a new access is proposed by disposing the residues using molten salt oxidation. A high salt content pharmaceutical residue that contains 28.82wt% Na has been selected as the sample. Molten salt oxidation experiments have been conducted in a lab-scale molten salt reactor using a ternary salt (Li,Na,K)2CO3. The experimental parameters investigated here are the temperature of molten salt and the excess air factor. The concentrations of the CO, NOx and SOx in the off-gas are monitored on-line. Results show that the concentration of CO decreases with temperature increasing, especially at temperature higher than 600̊C. The SOx in the off-gas has been detected rarely, irrespective of the operating conditions. When the temperature is below 700̊C, the concentrations of NOx in the off-gas are under 200ppm, but as the temperature reached 700̊C, due to the nitrite in salt bath begins to decompose, the concentration increases dramatically, suggests the operating temperature should below 700̊C in order to suppress the emission of NOx. Compared to the temperature's role, the effect on the residue's oxidation of the excess air factor is relative small. In the drained salt no char has been found and the XRD analysis shows that the main content of the salt is still (Li,Na,K)2CO3. The results of our study show molten salt oxidation is a promising alternative technology for the disposal of high salt content pharmaceutical residues from the chemical synthesis pharmaceutical industry, and it may be also suitable for other high salt content residues from the fine chemical industry, however, more research is needed to verify this possibility.