H2–rich gas production from leaves

Abstract

In order to obtain the most favorable pyrolysis process for producing the highest yield of syngas from a range of leaf plants, the techniques of slow pyrolysis, fast pyrolysis and microwave pyrolysis of apple tree leaves, bamboo leaves, cypress leaves, sycamore tree leaves, and winter green leaves were investigated. The results showed that microwave pyrolysis produced the highest gaseous product yields (hydrogen rich gas) on all the 5 different kinds of leaves The apple tree leaves, sycamore leaves and wintergreen leaves showed higher yields of gas products than bamboo leaves and cypress leaves across all forms of pyrolysis. The experimentally determined higher heating values (HHV) of bio-chars from different leaves ranged from 20 to 28 MJ/Kg, interestingly, which are comparable to some coals. For the same variety of leaves, the HHV of bio-chars via different pyrolysis processes did not change significantly. However, the HHV of bio-chars from different leaves behaved differently, with the bio-char from wintergreen leaves showing the highest HHV, which reached around 27 MJ/Kg; on the contrary, the HHV of bio-chars from bamboo leaves gave the lowest values, some 20–22 MJ/Kg. For the gaseous products, the total amount of H2, CO, CO2 and CH4 reached 95% from all 3 pyrolysis treatments. Importantly, compared with slow and fast pyrolysis, the microwave pyrolysis of different leaves shows the highest content of H2 and CO and the lowest contents of CO2. The HHV of gaseous products of different leaves, using the same pyrolysis treatment, showed similar values but noticeably different when the pyrolysis process is for the same leaves is changed. The HHV of gaseous products via microwave pyrolysis are the highest amongst the different pyrolysis processes with the gaseous products HHV via fast pyrolysis being the lowest. We therefore conclude that microwave pyrolysis is a highly effective and also a highly selective process for H2 rich gas production from natural leaves. Furthermore, the addition of acid, bases and salts as catalysts for the pyrolysis did not noticeably result in any significant activity and products changes during the microwave pyrolysis process.