Effects of variable amounts of volatiles in corncob on microwave co-pyrolysis of low-rank coal and corncob

•Amounts of volatiles in corncob affected microwave co-pyrolysis products.•Some volatiles in corncob transformed to tar, and others changed to char.•Low volatiles in corncob improved the aromaticity and microcrystal structure of char.•Lightness and stability of tar were promoted by reducing volatiles in corncob.