Investigation of Ni─Ca binary catalystic activities for production of light aromatics from catalytic pyrolysis of brown coal

Abstract

The pyrolysis behavior of Ni─Ca-loaded Yunnan brown coals (Shi Caoxing [SCX] and Guo Jiashan [GJS]) was studied in a fixed-bed reactor to investigate the effects of Ni, Ca, and Ni─Ca loading on the yields of the obtained liquids and light aromatic hydrocarbons. Structural variations of the prepared coal chars were characterized by the scanning electron microscope-energy dispersion X-ray, Fourier-transform infrared spectroscopy, X-ray diffractometer, Brunauer-Emmett-Teller analysis, and elemental analysis. The effects of the Ni, Ca, and Ni─Ca loadings on the tar yield and upgradation of pyrolysis tar were evaluated. The results revealed that the use of the Ni─Ca catalyst affords improved yields of the liquid products and tar. Furthermore, the light hydrocarbon liquids contents in the coal tar was improved with the use of the Ni─Ca catalyst. The heavy components and polycyclic aromatic hydrocarbons in the coal tar could be easy to convert into light hydrocarbon liquids (phenol, cresol, xylenols, and naphthalene) with the SCX brown coal pyrolysis. In contrast, the catalytic pyrolysis of GJS brown coal was inhibited by the Ni─Ca catalyst. The study revealed that the catalytic activity of the Ni─Ca catalyst greatly depends on the type of the coal substrate and was promoted or inhibited depending on the type of the brown coal. Highlights1. The content of light aromatic hydrocarbons is improved by Ni─Ca catalyst.2. The Ca promoter reacted with ash (S and Al) to form CaSO 4 , and CaAl 4 O 7 compounds.3. Phenols are the main components in the light aromatic hydrocarbons. 4. The catalytic activity of the Ni─Ca catalyst promoted or inhibited by coal rank.

Influence of coal treatments on the Ni loading mechanism of Ni-loaded lignite char catalysts

“…The XRD patterns of Ni metal in Ni-loaded lignite char catalysts in this study also correspond to the report by Chaiklangmuang et al 18 The occurrences of Ni metals on all catalysts could be explained by the fact that the Ni ions (Ni 2+ ) that were exchanged with the oxygen-containing functional groups (e.g., hydroxyl, carboxyl and metal-carboxylate groups) in the untreated coal and each treated coal were reduced by H 2 and CO and turned into Ni metal (Ni 0 ). 49,50 The H 2 and CO were generated by the decomposition of the aliphatic hydrocarbons, hydroxyl and carboxylate groups of Ni-loaded coal samples during pyrolysis at 650 C. 51,52 The decomposition of the aliphatic hydrocarbons, hydroxyl and carboxylate groups of Ni-loaded lignite coal samples were conrmed by the FTIR spectra of catalysts. In Fig.…”