Efficient production of lignin-based slow-release nitrogen fertilizer via microwave heating

Microwave heating was first introduced into the Mannich reaction to prepare lignin-based organic slow-release nitrogen fertilizers. The response surface method was applied to acquire optimal conditions (amount of ethylenediamine, microwave heating temperature and time) for lignin with high organic nitrogen content. FT-IR spectra result revealed that the organic nitrogen was successfully grafted into the macromolecular structure of lignin. Elemental analysis showed that the organic nitrogen content increased (4.11?7.26 %) in lignin with the ethylenediamine content (4.0?8.0 g) or temperature (60?80 ?C) or time (10?40 min) of microwave heating increased. By response surface analysis, the highest organic nitrogen content (7.84 %) was obtained under the condition (8.0 g ethylenediamine, 80 ?C, 40 min). Contact angle, scanning electron microscopy, particle size, zeta potential, and thermal analysis results showed that lignin-based nitrogen fertilizers exhibited good slow-release properties of nitrogen. In short, lignin could be efficiently converted into organic slow-release nitrogen fertilizers by microwave heating. The approach with short processing time and simple operation was a potential method for preparing lignin-based fertilizer. The experiment will help to promote the value-added application of TL in the agricultural field.

Automated summary

Microwave heating was utilized for the first time in the Mannich reaction to prepare lignin-based organic slow-release nitrogen fertilizers. Optimal conditions for high organic nitrogen content in lignin were determined using the response surface method. The study demonstrated that microwave heating can efficiently convert lignin into organic slow-release nitrogen fertilizers, showing potential for agricultural applications.