Separation of Sodium Oxalate from the Oxidation Products of Yallourn Coal with Oxygen

Abstract

The separation of sodium oxalate from the by-products such as sodium benzenepolycarboxylates(NaBC) and sodium carbonate in the oxidation of Yallourn coal (C 66.8% d.a.f.) has been studied by using the difference of solubilities in sodium hydroxide solutions. Solubilities of sodium 1, 2-, 1, 4-, 1, 2, 4-, 1, 2, 4, 5-, and 1, 2, 3, 4, 5-, benzenepolycarboxylates in sodium hydroxide solutions (10-'25% NaOH), were measured, and the solubility product (K⁰_sp) of 1, 4-NaBC was calculated by the extended Debye-Hückel expression. The solubilities of NaBC except for 1, 4-NaBC were in the range 7.0-58.7g/100g-10% NaOH solution, decreased with the increasing concentration of NaOH, and were in the order : 1, 2, 4->1, 2->1, 2, 4, 5->1, 2, 3, 4, 5->1, 4- (Tables 2-6). 1, 4-NaBC was practically insoluble in 25% NaOH solution (Table2). The solubilities of 1, 4- and 1, 2, 3, 4, 5-NaBC were not very dependent on temperature (Tables 2, 6). Solubility product (K⁰_sp) of 1, 4-NaBC, (4.8×10^-4) was obtained using solubililies in NaCl solutions (Table 7, Fig. 1).
Sodium oxalate was separated from the actual oxidation products of Yallourn coal. The oxidation products (a mixture of sodium oxalate, sodium carbonate, NaBC, and other intermediates) (113 g) were washed first with 25% NaOH solution (150 g), and then, twice with 10% NaOH solution (100 g) (Fig. 2). The residue was washed with a small amount of water and dried. Thus, sodium oxalate was recovered 95% from the oxidation product, and the purity of crude sodium oxalate was 90% as it contained iron oxide, sodium carbonate and etc.