ABSTRACT

Ethylene spent caustic with strong alkalinity, high chemical oxygen demand (COD) and toxicity could not be directly discharged without pretreatment. In this paper, the composition of spent caustic from a petrochemical enterprise was analyzed. Effects of oxidants, reaction temperature, pressure and residence time on the removal ratio of COD in the spent caustic were investigated. The oxidation reaction mechanism of main organic sulphides in the spent caustic was discussed. Results show that COD of the ethylene spent caustic is ∼ 24.5 g/L, the main compositions are S^2- and disulphides including a small amount of ketones and phenolic organics. The removal ratio of S^2- in spent caustic is up to 100%, and the removal ratio of COD is over 83% at 180 °C with the pressure of 2 MPa and residence time of 15 min using oxygen as an oxidant. Taking dimethyl disulphide as an example, dimethyl disulphide with HO• firstly produces methyl thiosulphonate and methyl sulphenic acid, then further oxidized to generate methanesulphonic acid, and the C–S bonds in the methanesulphonic acid were broken to generate sulphuric acid and formic acid. So the oxidative degradation products of organic sulphides are sulphuric acid, formic acid and a small amount of acetic acid.

摘要

具有强碱性、高化学需氧量（COD）和毒性的乙烯废碱未经预处理不能直接排放。本文对某石化企业废碱的成分进行了分析。考察了氧化剂、反应温度、压力和停留时间对废碱中COD去除率的影响。讨论了废碱中主要有机硫化物的氧化反应机理。结果表明，乙烯废碱的COD约为24.5 g/L，主要成分为S ^2-和二硫化物，包括少量的酮类和酚类有机物。^{S 2}的去除率-以氧气为氧化剂，在180 ℃、2 MPa压力、15 min停留时间下，废碱中COD去除率达100%以上，COD去除率达83%以上。以二甲基二硫化物为例，二甲基二硫化物与H2O•首先生成硫代磺酸甲酯和甲基亚磺酸，然后进一步氧化生成甲磺酸，甲磺酸中的C-S键断裂生成硫酸和甲酸。所以有机硫化物的氧化降解产物是硫酸、甲酸和少量的醋酸。