The regeneration gas used in the K-LTA zeolite dryer of the MTO plant is planning to be changed from high purity nitrogen to the top gas of the demethanizer tower with high ethylene content, which is helpful to energy saving and emission reduction. However, there is a risk of ethylene oligomerization and carbon deposition when the regeneration gas passes through the K-LTA zeolite. The reaction mechanism of ethylene oligomerization on the K-LTA zeolite surface must be clarified. DFT calculations showed that ethylene could be physically adsorbed on Si-OH, Al-OH, the incomplete α- and β-cage on [100]-D4R-e surface. Butoxide forms through ethylene dimerization by stepwise and concerted mechanisms first. Then the reaction of ethylene and butoxide to n-hexyloxide leads to the continued growth of the carbon chain. The oligomerization reaction barriers of rate-determining steps are between 1.65∼1.75 eV, which is more difficult to occur than other zeolites. The ethylene oligomerization reaction can be divided into stepwise polymerization path, concerted polymerization path and concerted butene path. kMC simulation found that the dominant reaction paths are different under different temperatures. When the regeneration temperature reaches 473K, trace n-butene is generated. At 513K, ethylene oligommerization occurs and carbon deposition is formed. The results put forward higher requirements for strictly controlling the temperature of the dryer to ensure the excellent performance of K-LTA zeolite.

MTO装置K-LTA沸石干燥器所用再生气拟由高纯氮气改为高乙烯含量脱甲烷塔顶气，有利于节能减排。但再生气通过K-LTA分子筛时存在乙烯齐聚和积碳的风险。必须阐明乙烯在 K-LTA 沸石表面齐聚的反应机理。DFT计算表明乙烯可以物理吸附在Si-OH、Al-OH、[100]-D4R-e表面不完整的α-和β-笼上。丁氧基首先通过逐步和协同机制通过乙烯二聚形成。然后乙烯和丁醇反应生成正己醇，导致碳链继续增长。限速步骤的齐聚反应能垒在1.65∼1.75 eV之间，比其他沸石更难发生。乙烯齐聚反应可分为逐步聚合路径、协同聚合路径和协同丁烯路径。kMC模拟发现，在不同温度下，主要的反应路径是不同的。当再生温度达到473K时，生成微量正丁烯。在513K时，乙烯发生齐聚并形成积碳。结果对严格控制干燥机温度以保证K-LTA沸石的优良性能提出了更高的要求。乙烯齐聚反应可分为逐步聚合路径、协同聚合路径和协同丁烯路径。kMC模拟发现，在不同温度下，主要的反应路径是不同的。当再生温度达到473K时，生成微量正丁烯。在513K时，乙烯发生齐聚并形成积碳。结果对严格控制干燥机温度以保证K-LTA沸石的优良性能提出了更高的要求。乙烯齐聚反应可分为逐步聚合路径、协同聚合路径和协同丁烯路径。kMC模拟发现，在不同温度下，主要的反应路径是不同的。当再生温度达到473K时，生成微量正丁烯。在513K时，乙烯发生齐聚并形成积碳。结果对严格控制干燥机温度以保证K-LTA沸石的优良性能提出了更高的要求。乙烯发生齐聚并形成积碳。结果对严格控制干燥机温度以保证K-LTA沸石的优良性能提出了更高的要求。乙烯发生齐聚并形成积碳。结果对严格控制干燥机温度以保证K-LTA沸石的优良性能提出了更高的要求。