昭通褐煤热溶衍生油催化转化制环烷烃燃料

Catalytic conversion of Zhaotong lignite thermal dissolution derived oil to cycloalkane fuels

  • 摘要: 以昭通褐煤(ZL)热溶衍生油(oilTD)为原料,考察了催化烷基化-加氢脱氧制备环烷烃燃料的反应机理及工艺过程。通过典型模型化合物筛选出烷基化性能最佳的分子筛催化剂并优化反应条件,在最佳反应条件下对热溶衍生油进行烷基化,以NiFeAlO2为催化剂对烷基化反应后的衍生油进行催化加氢脱氧以制备环烷烃燃料。结果表明,Hβ分子筛催化剂烷基化活性最高,在180 ℃以正己烷为溶剂氮气气氛下反应10 h,底物的转化率大于80%,产物中双环产物的选择性大于90%。在Hβ沸石催化烷基化和NiFeAlO2催化加氢脱氧后,oilTD中的酚类含量显著降低,产物主要由单环烷烃和双环烷烃组成。本研究为从褐煤制备高密度燃料技术的开发提供参考。

     

    Abstract: Low-rank coals are abundant and widely distributed in the world. However, their utilization is hindered by inherent characteristics such as high oxygen and moisture content, along with low calorific value. This study investigates the preparation of cycloalkane fuels from lignite, aiming to achieve clean and efficient utilization of these resources while expanding the supply of cycloalkane fuels, thereby enhancing energy security. Specifically, Zhaotong lignite thermal dissolution derived oil was utilized as the raw material for catalytic alkylation-hydrodeoxygenation process. Initially, phenolic model compounds were employed to probe the catalytic activities of various catalysts in the alkylation-hydrogenation of phenols. The optimum reaction conditions for catalytic hydrodeoxygenation and alkylation reactions were explored systematically. Then, the thermal dissolution derived oil was alkylated under the optimal reaction conditions. Following alkylation, NiFeAlOx is used as the catalyst for catalytic hydrogenation and deoxygenation to remove oxygen-containing functional groups from the alkylation products, thereby improving the stability and quality of the final hydrocarbon products. The results demonstrated that the Hβ zeolite catalyst, characterized by a silicon-aluminum ratio of 25, exhibited high catalytic activity for alkylation of phenols, the alkylation products are mainly ortho position products and cyclohexanol dehydration is the initial step of the reaction and the resulting cyclohexene is the alkylation reagent. In addition, the growth of alkyl side chains increases the spatial site resistance, leading to a decrease in the conversion of the reactants, and the interactions between phenolic compounds inhibit the alkylation reaction. The characterization of the molecular sieves indicated that Hβ molecular sieves have the largest specific surface area and mesopore volume and suitable acid centre sites for the alkylation reaction. The active components of NiFeAlOx exist in the form of Ni and FeNi3, and the introduction of Fe not only increases the dispersion of Ni and the content of oxygen vacancy but also enhances the acidity and H2 activation ability. In addition, electrons migration from Fe to Ni results in the formation of electron-rich Ni species and electron-deficient Fe species. The catalyst with Ni/Fe/Al ratio of 3∶0.5∶2.5 displayed the highest performance for hydrodeoxygenation of phenols. Under the conditions of 180 ℃, using n-hexane as solvent in nitrogen atmosphere for 10 h, the phenolic compounds conversion exceeding 80%, coupled with bicyclic product selectivity exceeding 90%. According to GC/MS analysis, approximately 60% of the phenolic monomers present in the pyrolysis derived oil were successfully converted into bicyclic products under these conditions. Subsequent processing revealed that after alkylation with Hβ zeolite and hydrodeoxygenation with NiFeAlOx, the relative content (RC) of phenolic compounds decreased significantly from 35.38% to 9.74%. Concurrently, the RC of alkanes surged from 8.52% to 42.18%, with monocyclic and dicyclic alkanes contributing 16.63% and 21.26%, respectively. After alkylation-hydrodeoxygenation of Zhaotong lignite thermal dissolution derived oil, phenolic compounds can be converted to monocyclic alkanes and bicyclic alkanes, with bicyclic alkanes dominating the content. These results indicate that phenols in thermal dissolution derived oil can be converted into dicyclic alkanes through alkylation-hydrogenation deoxygenation process, which provides a possibility for producing high-density liquid fuel from the soluble portions of lignite.

     

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