Abstract:

Using naphtha as raw material for cracking, the effects of adding sulfides and sulfur/phosphorus compounds on the coking behavior of thermal cracking were investigated. The morphologies and structures of the pretreated HP40 alloy specimen and coke deposits were characterized by Raman spectroscopy, XRD, SEM and XPS. The results showed that the addition of phosphide into the sulfide additives led to the change in the structure of coke deposits under the condition of continuous addition of additives into the feed. The method with continuous addition of sulfur/phosphorus-based compounds showed excellent anti-coking properties. The surface pretreatment with sulfur or sulfur/phosphorus-based compounds made the increase of Fe content in the oxide film on the specimen. So anti-coking effect was limited when the pretreatment method was applied. The coking inhibition property of the application of surface pretreatment with sulfide/phosphide followed by continuous addition of sulfur/phosphorus-based compounds were similar to that of the application of continuous addition of sulfur/phosphorus-based compounds in the feed. However, the combination method showed the better anti-coking effect during the initial cracking process. All the addition methods led to the increased amounts of amorphous coke in the coke layer and the decreased graphitization degree of cokes. The results of the low H/C ratios showed the highly condensed structure of the coke deposits during thermal cracking process. The addition of sulfur and sulfur/phosphorus-based compounds could influence the dehydrogenation reaction to some extent during the coke formation by reducing catalytic coking.

Key words: thermal cracking reaction, thermal cracking coking, sulfur-based radical intermediates, sulfur/phosphorus-based compounds, addition methods, oxidation film on alloy

摘要：

以石脑油为裂解原料，考察了硫化物和硫/磷化合物的添加方式对热裂解结焦行为的影响。采用Raman光谱、XRD、SEM和XPS等检测手段表征了HP40试样的氧化层和焦炭的形貌与结构。结果表明，原料连续注入硫化物条件下，磷化物的加入使得焦炭结构改变，显示出优异的抗结焦效果。硫化物和硫/磷化合物预处理导致氧化层中Fe含量升高，抑制结焦效果有限。硫/磷预处理与原料连续注入硫/磷化合物联合方式与原料连续注入硫/磷化合物方式的抗结焦效果接近，但前者在初期的抑制效果更明显。所有添加方式都会引起结焦层中无定形焦炭含量升高，焦炭的石墨化程度降低。热裂解焦炭缩合程度较高，硫化物和硫/磷化合物减少了催化结焦的生成，在一定程度上提高了焦层中氢含量。

关键词: 热裂解反应, 热裂解结焦, 硫化物自由基, 硫/磷化合物, 添加方式, 合金氧化层