## 1 Introduction  
Over the last 15 years, the use of biomass from agricultural waste for the production of fuels and for obtaining chemical products has become more relevant. The use of biomass generates a closed cycle of greenhouse gases (SO\({}_{\times}\) NO\({}_{\times}\), and CO\({}_{\times}\)) [1,2]. On the other hand, pyrolysis is an innovative technique in the production of hydrocarbons from biomass. This process is the thermal decomposition of biomass in an inert atmosphere. Pyrolysis produces biochar, non-condensable gases, and a pyrolytic liquid called bio-oil or tar with fuel oil properties. The liquid fraction is obtained from condensable gases [3; 4; 5]. Bio-oil obtained from pyrolysis is a complex mixture of organic compounds obtained from the decomposition of biomass (cellulose, hemicellulose, and lignin). This is a mixture of organic compounds such as acids, aldehydes, esters, alcohols, ketones, anhydrosaccharides, levoglucosan, phenolic monomers, furans; additionally, from this mixture other chemicals can be obtained by hydrocarbons or hydroprocessing. Bio-oil can be used in the production of value-added chemicals or as a substitute for petroleum oils [6; 7; 8; 9].  
The microwave heating in biomass pyrolysis has created a great deal of interest due to its advantages over conduction heating: (1) heating is generated from inside the material and not from the outside as it happens with conduction, (2) there is less heat loss due to the transfer of electromagnetic energy instead of heat energy, (3) The heating is selective and without direct contact, which produces changes in the selectivity. In addition, microwave pyrolysis of biomass generates bio-oils with higher content of phenols and levoglucosan in comparison with conventional heating [10; 11; 12]. Microwaves are electric and magnetic fields perpendicular to each other. When these waves interact with a material they can be transmitted, reflected, or absorbed. Due to these interactions, the materials can be classified into three types (Figure 1): (I) transparent (microwaves go through the material without interactions), (II) opaque or conductive (microwaves are reflected and therefore do not penetrate the material), and (III) Absorbents (the material absorbs microwaves and it is heated) [13; 14; 15; 16]. The biomass is a transparent material to the microwaves and it must be mixed with an absorbent material for promoting the conversion of microwaves into heat. Some materials have the advantage of absorbing microwaves and transform the electromagnetic energy into heat, some of them are oxides (CuO, Fe\({}_{3}\)O\({}_{4}\), Ni\({}_{2}\)O\({}_{3}\)), carbon, and salts (FeS, CuS, CuCl) [17; 18; 19]. The CuO is a good microwave absorbent and it has shown a high selectivity for semi-volatile compounds. In the pyrolysis of pine sawdust with conduction heating, CuO has generated the highest efficiency of semi-volatile compounds compared with 31 catalysts including clays, metal oxides and zeolites. It is for this reason that CuO is proposed as a microwave absorbent [18].  
The sugarcane bagasse is proposed as a source of biomass, this is a waste that is produced in the order of millions of tons annually. The sugar cane occupies third place in the agricultural products in the world, and it is estimated that for each ton of sugarcane 280 kg of bagasse are generated [20; 21; 22].  
Three different methods were employed to synthesize the copper oxide: microwave, ultrasound, and a combined mode of microwave-ultrasound irradiation. These methods generate differences in the morphological and textural properties of the synthesized materials for the analysis in the pyrolysis. On the other hand, it is expected the optimization in the production of the liquid fraction (bio-oil) taking two references: the pyrolysis without absorbent and the use of CuO synthesized with heating conduction.  
Figure 1: Classification of materials according to their interaction with microwaves.