| Coal pyrolysis is an important step of clean and efficient classification utilization. How to convert the abundant coal resources with enriched hydrocarbons into high value-added products such as tar, gas and char has become an significant pressing topic in the field of energy. Different pyrolysis technology has developed presently, however, these pyrolysis processes were not yet mature. Apart from some engineering problems in process of industrialization, for example tar had high dust contents and the tar was easy cooled to block the pipelines, the coal structure was not correlate to its reactivity availably as for its complicated structure. The research was still limited in improving the efficiency of the pyrolysis processes by raising the high value-added tar quality and yield. Based on this,a novel catalytic pyrolysis concept, i.e., coal catalytic depolymerization was proposed by our research group, in which the catalyst was tried to add in the coal molecular structure by adding some adjunct reagents, and this is different from common catalytic pyrolysis where the catalysts is added on the outside surface of coal. And by this way, more high valued tar areexpected to be obtained. On the basis of previous research, the present paper studied the composition of minerals in coal and the influence of catalysts for coal catalytic depolymerization.In this work, Zaozhuang coal was chosen as an experimental sample and adopted with flotation separation method so as to remove the external minerals. Then Zaozhuang demineralized coal was obtained called ZZDM.By exploring the composition, the products distribution, the main mineral elements and the structure changes of ZZ and ZZDM, the synergistic effect between the minerals in coal and different catalysts was studied.Firstly, the external minerals were removed from 41.6% to 3.26% by using the flotation separation method. The tar yield of ZZ coal was 15.52%(daf), and ZZDM tar yield was 16.84%(daf). It was found that the content of light components of tar yielded from raw coal was higher than that from demineralization coal, the results showed that minerals in coal can cause secondary cracking of tar, produce more light fractions and improve the quality of the tar. Further analyses found that functional groups containing sulfur and oxygen were accelerated to crack with the action of minerals,which led to the increase of heteroatom species in raw tar. In addition,it showed the average pore diameter of raw coal was smaller than that of demineralization coal; emitting velocity of tar was slow during the process of pyrolysis, longer contact time with mineral made tar prone to crack.Therefore the pyrolysis tar yield of demineralization coal was higher thanthe raw coal.Secondly, the influence of the products distribution of catalytic depolymerization was investigated by adding different mass fraction Co-based and Ni-based catalysts into ZZ and ZZDM coal. The tar yield of ZZ and ZZDM coal showed a trend of increasing after the first drop. When Co-based mass fraction was 0.6%, tar yield of raw coalreached 19.99%(daf),the highest increase of 4.47%; and when Ni-based mass fraction was 0.8%,raw coal tar yield reached 19.62%(daf), the highest increase of 4.10%.Generally the tar yield of ZZDM coal was lower than that of ZZ coal.Combined with the tar component analysis, the influence of gas production and pyrolysis carbocoal rate, it showed that catalysts and minerals had synergy effect on coal catalytic depolymerization.Finally, it observed the effects of Fe-based, Al-based and Zn-based catalysts added into the raw coal. The results suggested that functional groups in coal structure containing oxygen were accelerated to crack into the tar when the Fe-based, Al-based and Zn-based catalysts were added.This research indicated the synergy influence between minerals in coal and catalyst for coal catalytic depolymerization. It needed comprehensive consideration of minerals in coal and catalyst effects for screening catalysts of increased tar yield in the future. |
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