洁净煤技术

2019, (05) 66-72

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煤焦油加氢油品中重质芳烃的溶剂萃取规律
Solvent extraction rules of heavy aromatics in productsgenerated by hydrogenation of coal tar

赵渊;王光耀;
ZHAO Yuan,WANG Guangyao

摘要(Abstract):

为研究煤焦油中重质芳烃的溶剂萃取规律,以煤焦油加氢产品中220~270℃馏分为原料,分别进行单一溶剂、复合溶剂、单级萃取以及多级萃取试验。结果表明,6种单一萃取剂中,N,N-二甲基甲酰胺(DMF)对芳烃的溶解性最佳,重质芳烃分配系数高达0.28,萃余相中的芳烃含量从原料的40.00%降至10.65%。二甲亚砜(DMSO)萃取重质芳烃的分配系数虽然与环丁砜(SULF)相当,但其分离因数高达75.00%,对重质芳烃具有较好的选择性。DMSO、DMF均属于非质子型极性溶剂,其介电常数和偶极矩均较大,因此极性较强,对于芳烃的溶解性及选择性均优于TRIG。其中,DMF含有N—C及CO基团,溶解能力较强,但通常含—S—基团的溶剂有较好的选择性,因此DMS选择性优于DMF,但同时由于DMSO中含有SO共轭双键基团,因此DMSO对芳烃的溶解性仅次于DMF。以DMSO为主萃取剂,添加20%DMF助剂进行复合溶剂萃取试验时,重质芳烃的分配系数从单萃取剂的0.09升至0.15,分离因数从单萃取剂的74.49%降至53.45%,重芳烃的萃取效率有所增加,但也增加了部分环烷烃的损失。经复合溶剂三级萃取最终可将总重质芳烃含量降至8.7%,其中二环芳烃与三环芳烃较易脱除,而单环芳烃含量仍高达8.20%。一环芳烃中茚满类、四氢萘类含量从原料的18.20%降至2.80%,总萃取率为84. 60%;茚类的含量从原料的14. 90%降至1. 30%,总萃取率为91.30%,而烷基苯原料中含量为6.70%,经过三级萃取后,降至4.10%,总萃取率仅为38.80%。影响萃取效果的主要原因是单环芳烃中烷基苯类化合物较难被常规极性溶剂萃取。C9以上一环芳烃中的烷基苯主要结构特点是苯环侧链上带有较长的链烷基或环烷基,如苯基环己烷、甲基苯基环己烷等,一方面其分子结构中苯环上的非芳烃侧链较长或结构较复杂,与主萃取剂DMSO的结构差异较大,另一方面烷基苯的极性与四氢萘、茚类等其他一环芳烃化合物的极性相比,其与DMSO极性的差距更大,因此无论从结构还是极性来说,烷基苯在DMSO中的溶解性均弱于四氢萘类以及茚类。
In order to study the solvent extraction law of heavy aromatic hydrocarbons in coal tar,the experiment of single solvent,compound solvent,single stage extraction and multistage extraction were carried out with the fraction of 220 to 270 ℃ in products generated by hydrogenation of coal tar as raw material. The results show that N,N-dimethylformamide (DMF) has the best solubility for aromatics among the six kinds of single extractants,the distribution coefficient of heavy aromatics is as high as 0.28,and the content of aromatics in the residual phase decreases from 40.00% of raw materials to 10.65%. Although the distribution coefficient of heavy aromatic hydrocarbons extracted by dimethyl sulfoxide (DMSO) is equivalent to that of sulfolane (SULF),the separation factor is as high as 75.00%,whichhas good selectivity for heavy aromatics. The DMSO and DMF belong to non-proton polar solvents,and the dielectric constant and dipole moment are larger,so the polarity is stronger,and their solubility and selectivity to aromatics are better than TRIG. The DMF contains N—C and conjugated double bond group,the solubility of DMSO to aromatics is only inferior to that of DMF. When the blended solvent extraction experiment is carried out with DMSO as the main extractant and 20% DMF as assistant,the distribution coefficient of heavy aromatic hydrocarbons increases from 0.09 of the single extractant to 0.15,the separation factor decreases from 74.49% of the single extractant to 53.45%,and the extraction efficiency of heavy aromatics increases,but it also increases the loss of some cycloparaffin. The total heavy aromatics content decreases to 8.70% through three stages extraction of compound solvent,and the bicyclic aromatics and tricyclic aromatics are easier to be extracted,but the content of mono cyclic aromatic hydrocarbons is still as high as 8.20%. The content of the indan and tetralin in the mono aromatic hydrocarbons decreases to 2.80% from 18.20% of the raw materials and the total extraction rate is 84.60%. The content of indene is reduced from 14.90% to 1.30%,and the total extraction rate is 91.30%. However,the content of alkylbenzene in raw materials is only 6.70%. Through three stages extraction,the content of alkylbenzene dropps to 4.10%,and the total extraction rate is only 38.80%. The main reason for the low extraction efficiency is that alkylbenzene compounds in mono aromatic hydrocarbons are difficult to be extracted by conventional polar solvent. The main structural characteristics of alkylbenzene in the first ring aromatic hydrocarbon above C9 are that the side chain of benzene ring has long alkyl or naphthenic groups,such as phenyl cyclohexane,methyl phenyl cyclohexane,etc. For one thing,the side chains of non-aromatic hydrocarbons on the benzene ring are long or complex,which are quite different from the main extractant DMSO. For another thing,compared with the polarity of other cyclic aromatic compounds such as tetrahydronaphthalene and indene,the polarity of alkylbenzene has a greater difference with that of DMSO. Therefore,the solubility of alkylbenzene in DMSO is weaker than that of tetrahydronaphthalene and indene due to the difference of structure or polarity.

关键词(KeyWords): 煤焦油;重质芳烃;复合溶剂;多级萃取
coal tar;heavyweight aromatic hydrocarbon;compound solvent;multi stage extraction

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作者(Author): 赵渊;王光耀;
ZHAO Yuan,WANG Guangyao

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