## 1 Introduction
However, the handling of digestate and the leakage of methane during biogas production can greatly increase greenhouse gas emissions, which may offset the environmental benefits [15; 16; 17]. Biogas reforming refers to the process of converting biogas into hydrogen through a series of chemical reactions [18]. [PERSON] et al. (2015, 2020) investigated biogas steam reforming using palladium-based membrane reactors and reported enhanced hydrogen production and separation efficiency [19; 20]. Increased pressures, temperatures, and steam-to-methane ratios enhance recovery and conversion rates. Figure 1 shows the biogas reforming, which consists of three main steps: (1) synthesis gas (SG) generation, (2) the water-gas shift (WGS) reaction, and (3) hydrogen purification [21]. In the first stage, the steam-biogas mixture undergoes catalytic reforming to produce syngas, primarily composed of hydrogen, carbon dioxide, carbon monoxide, methane, and water vapor. After the reformer, syngas (SG) is fed into a water-gas shift (WGS) reactor, where carbon monoxide (CO) combines with water (H\({}_{2}\)O) over a catalyst to produce hydrogen (H\({}_{2}\)) and carbon dioxide (CO\({}_{2}\)). This reaction is typically carried out in two stages: a lower temperature shift (LTS) reactor at 200-300 \({}^{\circ}\)C and a higher temperature shift (HTS) reactor at 300-400 \({}^{\circ}\)C [11]. Methane (CH\({}_{4}\)) reacts with steam (H\({}_{2}\)O) and carbon dioxide (CO\({}_{2}\)) to produce synthesis gas (SG), which contains hydrogen (H\({}_{2}\)), carbon monoxide (CO), carbon dioxide (CO\({}_{2}\)), methane (CH\({}_{4}\)), and water (H\({}_{2}\)O), among other components. The general equation for biogas reforming is presented in Equation (1). \[\text{BG}\ \Big{(}\text{CH}_{4}+\alpha\text{H}_{2}\text{O}_{\text{(steam)}} \Big{)}+\beta\text{CO}_{2}\ \rightarrow\ \text{SG}\ (\text{H}_{2},\text{ CO},\text{ CO}_{2},\text{ CH}_{4},\text{ H}_{2}\text{O},\text{ etc.}) \tag{1}\]  
where \(\alpha\) and \(\beta\) are the stoichiometric coefficients of water and carbon dioxide, respectively. The main possible reactions in biogas reforming are steam methane reforming (SMR: Equation (2)), dry methane reforming (DMR: Equation (3)), and water-gas shift (WGS: Equation (4)). Steam methane reforming (SMR): Methane reacts with steam to form carbon monoxide and hydrogen gas, with an enthalpy change of +206.11 kJ/mol:  
\[\text{CH}_{4}+\text{H}_{2}\text{O}\ \leftrightarrow\text{CO}+3\text{H}_{2}\ \Delta\text{H}_{298\text{K}}^{\circ}=+206.11\ kJ/mol \tag{2}\]  
Dry methane reforming (DMR): Methane from biogas reacts with carbon dioxide to form carbon monoxide and hydrogen, with an enthalpy change of +247.28 kJ/mol:  
\[\text{CH}_{4}+\text{CO}_{2}\ \leftrightarrow 2\text{CO}+2\text{H}_{2}\ \Delta\text{H}_{298\text{K}}^{\circ}=+247.28\ kJ/mol \tag{3}\]  
Water-gas shift (WGS) reaction: Carbon monoxide reacts with steam to produce carbon dioxide and hydrogen, releasing \(-41.17\ kJ/mol\) of energy:  
\[\text{CO}+\text{H}_{2}\text{O}\ \leftrightarrow\text{CO}_{2}+\text{H}_{2}\ \Delta\text{H}_{298\text{K}}^{\circ}=-41.2\ kJ/mol \tag{4}\]  
Carbon formation reactions: During the process, a specific side reaction contributes to the creation of coke. Boudouard reaction: Carbon monoxide decomposes into carbon dioxide and solid carbon (graphite), releasing \(-172.43\ kJ/mol\) of energy (Equation (5)):  
\[2\text{CO}\ \leftrightarrow\text{CO}_{2}+\text{C}_{\text{(graphite)}}\ \Delta\text{H}_{298\text{K}}^{\circ}=-172.43\ kJ/mol \tag{5}\]  
Figure 1: A detailed flowsheet of the H\({}_{2}\) production process from biogas reforming [21].