Co-pyrolysis characteristics and synergistic mechanism of low-rank coal and direct liquefaction residue

ABSTRACT

In this study, the co-pyrolysis of low-rank pulverized coal (SJC) and direct liquefaction residue (DCLR) was comparatively examined. The structure and composition of tar and the evolution characteristics of gas during pyrolysis were analyzed through GC-MS, TG-FTIR, and other analytic techniques. Results showed that SJC+DCLR co-pyrolysis exhibited a significant synergistic effect. SJC and DCLR served as hydrogen donors to facilitate the hydrogenation of small molecular free radical fragments through pyrolysis, which increased the tar yield by 5.55%. Aromatic hydrocarbon and phenol contents in tar decreased by 11.88% and 7.94%, respectively, and alkane content increased by 12.25%. H₂ content in gas decreased by 19.05%, and CH₄ content increased by 19.60%. Co-pyrolysis could be divided into three stages. In the first stage, adsorbed water and CO₂ were removed at room temperature to 344.91°C, and the weak chemical bond between SJC and DCLR began to break. In the second stage, SJC and DCLR became pyrolyzed, small molecular free radical fragments were hydrogenated, large amounts of tar and small-molecule gases were produced at 344.91–643.35°C, and synergistic effect was primarily observed. In the third stage, condensation reaction occurred between small molecular free radical fragments at 643.35–845.75°C, thereby producing solid coke and a small amount of gas.

KEYWORDS:

• Low-rank coal
• direct coal liquefaction residue
• co-pyrolysis
• GC-MS
• TG-FTIR

Highlights

1. Interaction was presented in co-pyrolysis process and changed yield and composition of products.

2. Synergistic effects between low-rank coal and direct liquefaction residue are significant.

3. Synergy mainly occurred in the second stage (344.91-643.35°C).

4. The mechanism and reaction process of co-pyrolysis of low-rank coal and DCLR were proposed.

5. Co-pyrolysis of DCLR and low-rank coal would be a promising approach to better use of them.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [51774227];Major basic research Program of Shaanxi Natural Science Foundation [2017ZDJC-33] and Key Program of Shaanxi Natural Science Foundation [2018JZ5011].