Glycerol conversion into value-added products in presence of a green recyclable catalyst: Acid black carbon obtained from coffee ground wastes

•High catalytic activity of the green acidic carbon in glycerol etherification reaction.•Acid carbon preparation: an efficient approach for the valorization of coffee wastes.•Feasibility study of sulfonation of carbon from wastes transforming into good catalyst.•High stability of the surface groups which results in good reuse capacity of carbon.