**7. Conclusions**

SCWG is an innovative and potential treatment method for black liquor from pulping processes. Several researchers have studied this topic, and many progresses had been made, such as:


*Recent Advances in Supercritical Water Gasification of Pulping Black Liquor for Hydrogen... DOI: http://dx.doi.org/10.5772/intechopen.105566*

degradation, and the reduced metal can also serve as the catalyst. The combination of different metal oxides, such as CuO-ZnO, CeO2-ZrO2, and Fe2O3-Cr2O3, can further improve catalyst activity.


Though great progress has been made in SCWG of black liquor, several challenges still need to be handled before its industrial utilization. For example, reactor corrosion can be affected by the operating parameters, reactor materials, and properties of the feedstock. The alkali salts in black liquor were found to be able to aggravate the reactor corrosion. In addition, reactor plugging was another challenge to be overcome for continuous running of the system. Both the char generated for incomplete gasification and alkali salt precipitation in SCW can result in reactor plugging. Furthermore, though the distribution of the alkali salts in SCWG was revealed, the development of the proper method and equipment for the alkali recovery was still needed to improve the economic efficiency of this technology.

## **Acknowledgements**

The authors are grateful for the financial support from Fundamental Research Funds for the Central Universities (xzy012020072).
