Evolution of oxygen-containing functional groups on coal char surface during gasification in H2O/CO2.

Gasification converts coal into syngas (CO and H 2) for downstream utilization. The most important reaction in an autothermal gasifier is the char−H 2 O/CO 2 reaction. The evolution of C(O) complexes on the coal char surface directly determines the pathways and rates of CO and H 2 generation. This study mainly used a fixed bed reactor to prepare Zhundong coal char with different reaction levels in H 2 O and CO 2 , and its surface carboxyl, lactone, phenolic hydroxyl, and hydroxyl functional groups were systematically analyzed by using Boehm titration, FT-IR, and XPS. The results show that the contents of the four oxygen-containing groups in raw coal are in the order of carboxyl＞lactone＞phenol hydroxyl＞hydroxyl. In H 2 O gasification, the lactone groups were more susceptible to H 2 O resulting in a significant increase in carboxyl content at the early stage of the reaction. The hydroxyl, as a very active group in the reaction, and the amount of its generation and consumption was very obvious. The phenolic hydroxyl−the least thermally stable group among these four types of groups, was unable to participate in the inter-transformation between oxygen-containing functional groups during the gasification. During CO 2 gasification, the hydroxyl was rapidly consumed at the initial stage of the reaction and then shown a slow growth trend, and the newly generated hydroxyl would continue to undergo dehydrogenation to form new functional groups. At the end of the reaction, the transformation of other oxygen-containing functional groups into more stable carbonyl groups leads to a sudden increase in the content of carboxyl and lactone. In this work, Boehm titration was introduced into the determination of oxygen-containing functional groups on the surface of char during gasification in H 2 O/CO 2. • Evolution of oxygen-containing functional groups on coal char surface during gasification was revealed. • The evolution of oxygen-containing groups in H 2 O/CO 2 was significantly different. • H 2 O has more noticeable effect in increasing aromatic C=C of char than CO 2 during gasification. [ABSTRACT FROM AUTHOR]