# Advances in Bio-Hydrogen Production: A Critical Review of Pyrolysis Gas Reforming
## 4 Main Results  
This literature review of the two-stage catalytic reforming of pyrolysis volatiles demonstrates that this approach can significantly enhance hydrogen production, when compared to the single pyrolysis process. This significant increment in hydrogen production originates from two reasons: first, reforming pyrolysis volatiles, including condensable and non-condensable components, increases gas products and allows tuning the component distribution; second, the possibility to use different types of reactors for the reforming gives additional flexibility for increasing the hydrogen concentration in the products. The main findings of studies about the two-stage reforming of pyrolysis volatiles process are summarized in Tables 5 and 6, respectively. It is worth remarking that the reported studies in Table 6 were conducted at the laboratory scale.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Feedstock** &
\begin{tabular}{c} **Pyolysis Temperature**\({}^{\circ}\)**C** \\ **(Heating Rate**\({}^{\circ}\)**C/min)** \\ \end{tabular} & **Scale** & **Total Gas Yield (wt.\%)** & **H\({}_{2}\) Yield (vol\%)** & **Ref.** \\ \hline \hline
**Slow pyrolysis** & & & & & \\ \hline Pine & 1600 (50) & Lab scale & 55 & 41.7 & [85] \\ \hline Cypress wood & 600 (30) & Lab scale & 11 & 14.4 & [86] \\ \hline Sugar cage bagasse & 480 (20) & Lab scale & 25 & 9.6 & [52] \\ \cline{2-6}  & 780 (20) & & 36 & 28.8 & \\ \hline  & 500 (30) & & 63 & 40.6 & \\ \cline{2-6}  & 550 (30) & & 63.4 & 47.8 & \\ \cline{2-6}  & 600 (30) & & 65.6 & 52.5 & \\ \cline{2-6}  & 650 (30) & & 67.8 & 54.2 & \\ \cline{2-6}  & 700 (30) & & 71.3 & 53.6 & \\ \cline{2-6}  & 750 (30) & & 74.3 & 53.4 & \\ \cline{2-6}  & 800 (30) & & 76.5 & 52.5 & \\ \hline Rice husk & 800 (2) & Lab scale & 25.5 & 8.6 & [87] \\ \hline Olive stone & 600 & Lab scale & 44.17 & 29.47 & [40] \\ \hline \hline
**Intermediate pyrolysis** & & & & & \\ \hline Agricultural residue & 500 (50) & Lab scale & 32 & 2.5 & [88] \\ \hline Brewers spent grain & 450 (100) & Lab scale & 21 & 1.6 & [89] \\ \hline
**Fast pyrolysis** & & & & & \\ \hline \hline \multirow{4}{*}{Sugar cane bagasse} & 480 (120) & & 14.12 & 8.7 & \\ \cline{2-6}  & 580 (120) & Lab scale & 15.46 & 15.2 & \\ \cline{2-6}  & 680 (120) & & 17.94 & 45.3 & \\ \hline \multirow{4}{*}{Beach wood} & 350 (1000) & & 10 & 0.9 & \\ \cline{2-6}  & 400 (1000) & & 18.4 & 1.4 & \\ \cline{2-6}  & 450 (1000) & & 10.1 & 0.8 & \\ \cline{2-6}  & 500 (1000) & Lab scale & 17.7 & 2.3 & \\ \cline{2-6}  & 550 (1000) & & 20.5 & 3.4 & \\ \cline{2-6}  & 800 (1000) & & 56.9 & 13.8 & \\ \hline Pine & 550 (1000) & & 17.9 & 6.9 & \\ \hline Bamboo & 500 (1000) & & 19.1 & 1.5 & \\ \hline \multirow{4}{*}{Pine wood} & 440 (N.A) & & 61.5 & 4.2 & \\ \cline{2-6}  & 460 (N.A) & & 62.6 & 4.9 & \\ \cline{2-6}  & 480 (N.A) & & 65.9 & 6.1 & \\ \cline{2-6}  & 510 (N.A) & & 64 & 7 & \\ \cline{2-6}  & 525 (N.A) & & 63.4 & 9.1 & \\ \cline{2-6}  & 565 (N.A) & & 61.5 & 15.1 & \\ \hline \multirow{4}{*}{Sawdust} & 400 (N.A) & & 23.7 & 10 & \\ \cline{2-6}  & 450 (N.A) & & 22.1 & 20 & \\ \cline{2-6}  & 500 (N.A) & & 15.2 & 24 & \\ \cline{2-6}  & 550 (N.A) & & 22.7 & 21 & \\ \cline{2-6}  & 600 (N.A) & & 26.7 & 19 & \\ \hline
**Flash pyrolysis** & & & & & \\ \cline{2-6} Palm kernel shell & 600 (N.A) & Lab scale & 5 & 18.5 & \\ \cline{2-6}  & 900 (N.A) & Lab scale & 32 & 26.6 & \\ \hline \hline \end{tabular} Note: NA: not available.  
\end{table}
Table 5: Hydrogen yield reported in different research studies of pyrolysis process.