Composition and structure of extraction residue of direct coal liquefaction residue and recycle of active phase of iron catalyst

In order to solve the problem of iron source supply for large-scale direct liquefaction catalyst, and meanwhile realize the harmless separated-utilization of extraction residue from coal liquefaction, this paper conducted a research on the recovery of iron catalyst from extraction residue, and explored the feasibility of enriching recovery of iron catalyst by using physical magnetic separation method. Firstly, the characterization methods, such as particle size analysis, XRF, XRD, SEM, TG, SEM-EDX, were used to comprehensively characterize and analyze the physical and chemical properties of the extraction residue, and therefore determine the contents and existence forms of iron catalyst. From the results analysis, it can be seen that the extraction residue from industrial equipment is mainly composed of carbon in unreacted coal and residual carbon, volatile matter and ash, with uniform particle size and no agglomeration. The mass fraction of iron is 5.96%, and the iron species still exist as the active phase of paramagnetic Fe1-xS, which doped and coated by unreacted coal and residual asphalt, and uniformly mixed and distributed in the extracts with various elements such as Ca, Si, Al, O, etc. On this basis, four types of magnetic separation equipment were selected for magnetic separation enrichment under different magnetic field strengths, and the enriched samples were then used as catalysts for direct coal liquefaction reaction to investigate their performances in direct liquefaction reaction. The experimental results show that:On the one hand, the high gradient magnetic force generated by the wet vertical ring pulsating high gradient magnetic separator is applied to the magnetic catalyst fine powder. Together with using water as dispersion medium and washing medium, the fine separation of iron catalyst powder from extraction residue was realized more effectively. With the magnetic field strength of 640 000 A/m, the material enrichment rate of the iron-containing catalyst was 10.48%, and the mass fraction of iron was 11.37%, the extraction oil yield of high-pressure autoclave 41.96%, which was 7.17% higher than that without the catalyst, and 8.99% higher than that with the extraction residue. It can be mixed into fresh catalyst to achieve an effective reuse, to some extent solving the problem of catalyst iron source shortage. © 2024 China Coal Society. All rights reserved.