Abstract:

Zero discharge and resourcelization of high-salt sewage is one of the most significant approaches to solve the problem of water pollution and shortage. Solid Na₂SO₄ product is recovered from spent caustic of ethylene cracking by oil removal, decarbonization, concentration and cooling crystallization process. The experimental results show that coal-based activated carbon can be used as an excellent oil adsorbent, capable of removing more than 94% of oil. The process of sulfuric acid decarbonization can convert Na₂CO₃ and NaOH in spent caustic into Na₂SO₄, reduce the influence of impurity salt in cooling crystallization and increase the yield of Na₂SO₄. The concentration process can increase the yield of Na₂SO₄ product in the later stage of cooling crystallization. Cooling crystallization can obtain Na₂SO₄ products with good crystallinity over a wide temperature range(1～14 ℃), without the formation of impurities including NaCl. This work provides a guiding significance for zero emission and resourcelization of spent caustic.

Key words: cooling crystallization method, ethylene, spent caustic, sodium sulfate, total organic carbon, SEM, XRD

摘要：

高盐废水的零排放和资源化是解决水污染和水资源短缺问题的重要途径之一，通过除油、脱碳、浓缩、冷却结晶过程，从乙烯裂解废碱中回收得到固体Na₂SO₄产品。实验结果表明，煤基活性炭可作为优良的油吸附剂，能去除94%以上的油。硫酸脱碳过程可使废碱液中Na₂CO₃及NaOH转化为Na₂SO₄,减少冷却结晶中杂盐的影响，提高Na₂SO₄产率。浓缩过程可以提高后期冷却结晶Na₂SO₄产品的产率，冷却结晶可以在很宽的温度范围内(1～14℃)得到具有较好结晶度的Na₂SO₄产品，且不会形成包括NaCl在内的杂盐，表明通过冷却结晶工艺回收Na₂SO₄具有可行性。本研究结果可为废碱液的零排放和资源化处理提供借鉴。

关键词: 冷却结晶法, 乙烯, 废碱液, Na2SO4, 总有机碳, SEM, XRD