Abstract:

Objective: In the present work, the evolution of ash composition and transformation mechanism was interpreted in details. Importantly, the distribution pattern of silicon in internodes and nodes as well as the effects of gradient pyrolysis on the silicon deposition will be investigated. The above results will provide theoretical and data support for the development of efficient ash removal process as well as the production of high purity bamboo charcoal and bamboo activated carbon. Method: One-year-old moso bamboo (Phyllostachys edulis) was selected, and SEM-EDXA, XRF, XRD and other analytical techniques were used to study the changing rules of ash content and composition in different parts of bamboo (internodes, nodes, inner bark, outer bark and stomata) under the gradient pyrolysis conditions (350, 500, 800, and 1 000 ℃). Also, the combination of all these techniques were used to explore the distribution of silicon in the various parts of bamboo (inner and outer bark, stomata, bamboo green, bamboo timber, and bamboo yellow) and the effects of the pyrolysis treatment on the silicon distribution. Result: The ash of bamboo mainly consisted of CaO, K₂O, SiO₂, Al₂O₃, and certain sulfur oxides (SO₃) and phosphorus oxides (P₂O₅). XRD analysis showed that the ash of bamboo internodes was mainly composed of KCl, K₂SO₄, KAlSiO, KFeSiO₄, etc. In addition to the above inorganic salts, there were obvious crystalline SiO₂ characteristic peaks in the internodes. Silicon-containing inorganic salts, such as KAlSiO, and KFeSiO₄ were generated and short-range order of turbostratic stacks in bamboo charcoal occured when the pyrolysis temperature reaches 800 ℃ Higher silicon content was observed in the bark and stomata for both internodes and nodes. Besides the parenchyma near the epidermis containing silicon particles, the parenchyma located in bamboo timber and yellow also existed micrometers silicon oxides. The relative content of silicon reached the maximum at 500 ℃, while the relative content of silicon began to decrease at 800 ℃ with the generation of silicate and aluminosilicate. The relative content of potassium showed a linear increase throughout the pyrolysis process. High-temperature heat treatment caused the volatilization of elements such as H and O, the consumption of carbon, resulting in the release of silicon which were deposited in the lumen of the vessel and parenchyma. Conclusion: 1) Bamboo nodes and internodes displayed the similar ash composition, while the internode parts had a higher silicon content. Silicon was widely distributed in the bamboo outer bark, stomata and parenchyma adjacent to bamboo green. 2) The relative content of CaO and K₂O in the nodes and internodes displayed the maximum value when the pyrolysis temperature reached 500 ℃ Increasing the pyrolysis temperature to 800 ℃ converted these inorganic salts into silicate and aluminosilicate. 3) High-temperature treatment caused the release of silicon in the internodes, which was deposited in the lumen of vessel and parenchyma.

Key words: moso bamboo (Phyllostachys edulis), high temperature pyrolysis, ash composition of bamboo, silicon distribution