Thermal stability of Na2SO3 and re-determination of the binary phase diagram Na2SO4-Na2S

摘要: Black liquors are presently combusted in recovery boilers where the inorganic cooking chemicals recovered and energy organic material is converted to steam electricity. A new technology, developed by Chemrec AB, black liquor gasification (BLG). BLG has more offer compared boiler process, terms of on-site generation electric power, liquid fuel process chemicals. prerequisite for both optimization existing processes commercialization better understanding physical chemical involved including interactions with refractory lining. The chemistry very complex minimize extensive expensive time-consuming studies otherwise required accurate reliable model descriptions needed a full most as well up-scaling processes. However, using these calculated results practice, errors state art thermochemical data have be considered. An literature review was therefore performed update unary, binary higher order systems. from reviled that there significant range uncertainty several condensed phases few gas species. This resulted experimental re-determinations phase diagrams sodium carbonate-sodium sulfide (Na2CO3-Na2S) sulfate-sodium (Na2SO4-Na2S) High Temperature Microscopy (HTM), X-ray Diffraction (HT-XRD) Differential Thermal Analysis (DTA). For Na2CO3-Na2S system, measurements were carried out dry inert atmosphere at temperatures 25 1200 °C. To examine influence pure CO2 on melting behavior, HTM experiments same temperature interval made. include re-determination liquidus curves, Na2CO3 rich area, points components determination extent solid solution, Na2CO3(ss), area. thermal stability Na2SO3 studied diagram Na2SO4-Na2S re-determined. indicate can exist short time up 750 °C, before it melts. It also proved solid/solid transformation, not reported earlier, occurs 675 ± 10 At around 700 gradually breaks down within hours, finally form Na2SO4 Na2S. From metastable Na2SO3, an equilibrium been constructed system Na2SO4-Na2S. Improved Na2S experimentally obtained solid-state EMF measurements. constant Na2S(s) determined log Kf(Na2S(s)) (± 0.05) = 216.28 – 4750(T/K)–1 28.28878 ln (T/K). Gibbs formation ΔfG°(Na2S(s))/(kJ mol–1) 1.0) 90.9 4.1407(T/K) + 0.5415849(T/K) standard enthalpy evaluated ΔfH°(Na2S(s), 298.15 K)/(kJ 369.0. entropy S°(Na2S(s), K)/(J mol–1 K–1) 2.0) 97.0. Analyses used gasifier elucidate Scanning electron microscopy (SEM) analysis revealed attack limited 250-300 μm, surface directly exposed smelt. XRD found this layer dominated sodiumaluminosilicates, mainly Na1.55Al1.55Si0.45O4.