Objective  Effect of processing temperature in pyrolysis of discarded tomato vines on the physiochemical properties of the resulting biochar was studied.

  Methods  Biochar of waste tomato vines were prepared under the pyrolytic temperatures of 300 ℃, 500 ℃, and 700 ℃ for 2h. Surface characteristics, element, and functional groups of the biochar were examined by means of electron microscope scanning, elemental analysis, and Fourier transform infrared spectrometer.

  Results   The biochar prepared under different pyrolytic temperatures had a pH ranging 9.83-10.67. High process temperature reduced the yield but increased the ash content of the biochar. At 500 ℃, the biochar had the least amount of total nitrogen, but the highest at 300 ℃. At 500 ℃, the fixed carbon content peaked at 51.42%, and the C/N ratio at 36.63. More pores appeared on the biochar made by a lower than a higher temperature, under which ash and/or molten elements tended to cover the surface reducing the porosity. A high pyrolytic temperature, comparing 700 ℃ to 300 ℃ or 500 ℃, also raised the aromatization, as shown by the declined Fourier transform infrared spectroscopy spectrum absorption, especially at 500-800cm⁻¹ region.

  Conclusion   The temperature applied in pyrolysis affected the physics, chemistry, and microstructure of the tomato vine biochar. Overall, a pyrolysis process of 300-500 ℃ for 2 h appeared to deliver desirable results.