常见钠盐的高温挥发特性及热解机理

doi:10.11949/0438-1157.20200061

摘要/Abstract

摘要：

选取有机废液中常见的钠盐(氯化钠、碳酸钠、硫酸钠、甲酸钠、乙酸钠、草酸钠)，通过热重分析仪，在25~1400℃考察其高温挥发特性。基于Gibbs自由能最小原理，对NaCl、Na₂CO₃及Na₂SO₄的挥发特性进行热力学计算。结果表明，在N₂气氛中，NaCl在达到熔点后以气态NaCl及气态Na₂Cl₂的形式释放，Na₂SO₄升温至885℃分解生成Na₂O，同时Na₂O分解，并以Na单质形式释放。而有机羧酸钠盐在600℃之前均热解为Na₂CO₃，继续升高温度则分解为Na₂O，同样最后以气态Na单质的形式释放。在空气气氛中，由于O₂的存在，抑制了Na₂O的分解反应，致使Na₂CO₃分解速率小于N₂气氛。

关键词: 钠盐, 高温挥发特性, 热重分析, 热解, 热力学, 腐蚀

Abstract:

The common sodium salts (sodium chloride, sodium carbonate, sodium sulphate, sodium formate, sodium acetate, sodium oxalate) in organic wastewater were selected, and their high-temperature volatility characteristics were examined by thermogravimetric analyzer at 25—1400℃. Based on the principle of Gibbs free energy minimum, the volatility characteristics of NaCl, Na₂CO₃ and Na₂SO₄ were calculated thermodynamically. The results showed that in the N₂ atmosphere, NaCl began to be released in the form of NaCl(g) and Na₂Cl₂(g) after reaching the melting point. Na₂SO₄ decomposed to form Na₂O at high temperature, and it continued to decompose to form elemental sodium when the temperature raised. The organic carboxylic acid sodium salt was pyrolyzed to Na₂CO₃ before 600℃, then it decomposed to form Na₂O when the temperature went up, and finally released as sodium vapor. In the air atmosphere, due to the presence of O₂, the decomposition reaction of Na₂O is suppressed, resulting in the decomposition rate of Na₂CO₃ is less than that of N₂ atmosphere.

Key words: sodium salt, high temperature volatility characteristics, thermogravimetric analysis, pyrolysis, thermodynamic, corrosion

中图分类号:

TQ 131.1

李剑, 蒲舸, 陈家善, 刘啟文. 常见钠盐的高温挥发特性及热解机理[J]. 化工学报, 2020, 71(8): 3452-3459.

Jian LI, Ge PU, Jiashan CHEN, Qiwen LIU. High-temperature volatility characteristics and pyrolysis mechanism of common sodium salts[J]. CIESC Journal, 2020, 71(8): 3452-3459.

图/表 7

图1 钠盐在氮气气氛下热解图谱

Fig.1 Pyolytic spectrum of sodium salts in nigrogen atmosphere

表1 钠盐的分解特性参数

Table 1 Pyrolysis characteristics of sodium salts

Compound	Fusion point/℃	Degradation stage
Compound	Fusion point/℃	Temperature interval/℃	Pyrolysis products	TG/%
NaCl	803	808—1153	NaCl(g),Na₂Cl₂(g)	100.0
Na₂CO₃	851	853—1280	Na₂O,Na(g)	69.9
Na₂CO₃	851	1280—1400	Na(g)	4.4
Na₂SO₄	885	1105—1400	Na₂O,Na(g)	21.5
HCOONa	226	372—440	Na₂C₂O₄，Na₂CO₃	12
		553—573	Na₂CO₃	7.5
		855—1260	Na₂O，Na(g)	31.4
		1260—1400	Na(g)	1.7
CH₃COONa	308	416—530	Na₂CO₃	34.2
		858—1232	Na₂O，Na(g)	35.4
		1232—1400	Na(g)	4.4
NaOOC—COONa	—	540—576	Na₂CO₃	17.6
		864—1190	Na₂O，Na(g)	45.1
		1190—1400	Na(g)	5.9

图2 Na2CO3在空气气氛下热解图谱

Fig.2 Pyolytic spectrum of Na2CO3 in air atmosphere

图3 Na2CO3在N2、空气气氛下热解图谱对比

Fig.3 Comparison of pyrolytic spectrograms of Na2CO3 under nitrogen and air atmosphere

图4 NaCl、Na2SO4平衡组分计算结果

Fig.4 NaCl/Na2SO4 equilibrium composition calculation

图5 Na2CO3平衡组分计算结果

Fig.5 Na2CO3 equilibrium composition calculation

图6 Na2O平衡组分计算结果

Fig.6 Na2O equilibrium composition calculation

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