固相萃取/气相色谱-质谱分析催化裂化柴油中的含氮化合物

Determination of Nitrogen Compounds in Fluid Catalytic Cracking Diesel by Gas Chromatography-Mass Spectrometry with Solid Phase Extraction

采用固相萃取技术分离富集催化裂化柴油中的中性和碱性含氮化合物,优化了洗脱溶剂的种类及用量,并考察了分离方法的回收率和重复性。结果表明,二氯甲烷和丙酮-二氯甲烷可以有效分离富集柴油中的中性和碱性含氮化合物;固相萃取法的回收率高达99. 5%,3次分离实验结果的相对标准偏差均小于4%。分离后的组分采用气相色谱-质谱(GC-MS)定性,数据表明,催化裂化柴油中的中性含氮化合物主要为C0～C3-吲哚及C0～C5-咔唑,碱性含氮化合物主要为C1～C4-苯胺及C0～C2-喹啉。采用气相色谱-氮化学发光检测器对含氮化合物进行定量,发现中性含氮化合物占已定性含氮化合物总量的96. 6%;咔唑类含氮化合物的含量最高,占已定性含氮化合物总量的64. 3%;从化合物结构上看,化合物含量随着甲基取代基数目的增多呈先增加后降低的趋势。该方法可用于催化裂化柴油中含氮化合物的类型分布分析。

A method of gas chromatography-mass spectrometry(GC-MS)with solid phase extraction was developed for the determination of nitrogen compounds in fluid catalytic cracking(FCC)diesel fraction.The neutral and alkaline nitrogen compounds in FCC diesel fraction were separated and concentrated by solid phase extraction(SPE)technique.The type and dosage of different elution solvents were optimized.It was found that dichloromethane and acetone-dichloromethane could effectively separate the neutral and alkaline nitrogen compounds in FCC diesel.The recovery and repeatability of the SPE method were investigated.Results showed that the recovery of the separation method was as high as 99.5%,and the relative standard deviations for the repeatability results of three separation experiments were less than 4%.The separated components were confirmed by gas chromatography-mass spectrometry(GC-MS).It was revealed that neutral nitrogen compounds generally consisted of C0-C3 indoles and C0-C5 carbazoles,while alkaline nitrogen compouns were made up of C1-C4 anilines and C0-C2 quinolines.The quantitation on nitrogen compounds was carried out by gas chromatography with nitrogen chemiluminescence detector(GC-NCD).Results showed that 96.6%of the identified compounds in FCC diesel attributed to the neutral compounds,in which the content of carbazoles was the highest,accounting for 64.3%of the total of the qualified nitrogen compounds.From the aspect of compound structure,the content of nitrogen compounds increased first and then decreases with the increase of the number of methyl substituents.In general,this method could be used in the analysis on the type distribution of nitrogen compounds in FCC diesel fraction.