Microwave–assisted hydrothermal conversion of crop straw: Enhancing the properties of liquid product and hydrochar by varying temperature and medium

•Optimized temperature and medium improve liquid and hydrochar quality and property.•Magnesium acetate increases carbon, acid, nitrogen and metal ions in liquid.•Acids increase function group, pore structure and carbon microsphere in hydrochar.•Magnesium acetate promotes ordered carbon structure, O/C and (N + O)/C of hydrochar.•Reaction pathways were explored based on product distribution and composition.