# Analysis of the Sugarane Biomass Use to Produce Green Hydrogen: Brazilian Case Study
## 5 Environmental Impacts and Sustainable Solutions
### Second-Generation Ethanol as a Sustainable Pathway for Green Hydrogen  
It is well-established that during the combustion of C\({}_{2}\)H\({}_{6}\)O, complete combustion produces CO\({}_{2}\) and water (H\({}_{2}\)O) (Reaction (1)). Considering the molar masses of carbon (12 g/mol), hydrogen (1 g/mol), and oxygen (16 g/mol) from the periodic table, we can infer that each mol of ethanol (46 g) produces two moles of CO\({}_{2}\) (88 g) during the process. Therefore, while 2G ethanol is a renewable biofuel, its combustion is not entirely environmentally friendly, as it releases CO\({}_{2}\) into the atmosphere. This highlights the need to convert C\({}_{2}\)H\({}_{6}\)O into another fuel whose complete combustion is green, i.e., which results in no pollutant emissions. Reaction (1):  
\[\text{C}_{2}\text{H}_{6}\text{O}+3\text{O}_{2}\to 2\text{CO}_{2}+3\text{H}_{2} \text{O} \tag{1}\]  
To address the issue of CO\({}_{2}\) emissions from ethanol combustion, there is the potential to produce green hydrogen, which is widely regarded as a key solution for the future renewable energy landscape. This can be achieved through parallel processes involving 2G ethanol. Hydrogen, in addition to being a clean and alternative fuel--since the only byproduct of its combustion is water (Reaction (2))--can be used to generate low-carbon renewable energy for applications such as urban transportation and stationary energy needs. Furthermore, it serves as a valuable raw material in industries such as steel, chemicals, petrochemicals, agriculture, and food production, among many others. Reaction (2):  
\[\text{H}_{2}+\frac{1}{2}\text{O}_{2}\to\text{H}_{2}\text{O} \tag{2}\]  
Based on a review of the existing literature on methods for producing green hydrogen, a diagram was created to summarize the main approaches for obtaining biohydrogen using second-generation ethanol or integrated processes (Figure 13). The diagram highlights that ethanol-based methods involve two primary pathways from a water-ethanol mixture: electrocatalytic reforming using a Ni-Cu bilayer of hollow microtubes and a plasma reactor driven by spark discharge, which is resistant to coking. For integrated production, three main approaches involving lignocellulosic biomass are outlined: fermentation coupled with energy generation technologies, the use of nanomaterials alongside established processing methods, and anaerobic bacterial cultivation with the addition of iron nanoparticles. Additionally, two other distinct approaches are noted: biohydrogen production within the framework of a circular biorefinery and through xylose conversion via acidogenesis. To further elucidate the key methods depicted in Figure 13, Table 3 provides a detailed comparison of the seven approaches for biohydrogen production. The table highlights the techniques, reported yields, advantages, and limitations associated with each method. This comparative analysis consolidates state-of-the-art knowledge while highlighting the unique contributions and practical implications of each approach. By summarizing the strengths and challenges of these methods, the table offers a comprehensive perspective on their potential applications and suitability for different contexts.