# Biochar as a Multifunctional Component of the Environment--A Review
## 2 Biochar and its Properties
High heating rates promote cellulose and hemicellulose depolymerization reactions, minimizing the volatiles residence time inside the particle and secondary reactions. It also favors the volatiles cracking. So, the condensable gas release goes on quickly thus achieving high yields of bio-oil and the lowest production of char. Low temperatures and low heating rates promote intra-chain hydrogen bonds of cellulose functional groups, increasing the probability of collision to produce a dehydration reaction. For high heating rates, inter-chain hydrogen bonds are stronger achieving greater separation between the cellulose molecules and thus decreasing the possibility of collisions that facilitate the dehydration reaction. There are many reports in literature pointing out the importance of the effects of the heating rate on the yields of bio-oil and char [22; 46; 47]. The physical and chemical properties of the raw materials used in the process are the most important. The highest yields of carbonization products are obtained when raw materials with high lignin content are subjected to pyrolysis at moderate temperatures. Basically, biomass containing a significant amount of volatile substances offers a large amount of pyrolytic gas and bio-oil, and the presence of solid coal increases the efficiency of biochar production [19]. The moisture content of \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Feedstock for** & **pH** & \begin{tabular}{c} **C g** \\ **kg\({}^{-1}\)** \\ \end{tabular} & \begin{tabular}{c} **N g** \\ **kg\({}^{-1}\)** \\ \end{tabular} & **C/N** & \begin{tabular}{c} **P g** \\ **kg\({}^{-1}\)** \\ \end{tabular} & \
\begin{tabular}{c} **K g** \\ **kg\({}^{-1}\)** \\ \end{tabular} & **Ash** &
\begin{tabular}{c} **Temp. of** \\ **Pyrolysis** \\ **(\({}^{\circ}\)C)** \\ \end{tabular} & **References** \\ \hline Acacia bark & 7.4 & 398 & 10.4 & 38 & – & – & – & 260–360 & [36] \\ Cocount & – & 690 & 9.4 & 73 & – & – & 3.38 & 500 & [37] \\ Corn & – & 675 & 9.3 & 73 & – & 10.4 & – & 350 & [38] \\ Corn & – & 790 & 9.2 & 86 & – & 6.7 & – & 600 & [38] \\ Green waste & 6.2 & 680 & 1.7 & 400 & 0.2 & 1 & – & 450 & [39] \\ Peanut shells & – & 499 & 11.0 & 45 & 0.6 & 6.2 & – & 400 & [40] \\ Pecan shells & 7.6 & 834 & 3.4 & 245 & – & – & 3.8 & 700 & [41] \\ Pecan shells & – & 880 & 4.0 & 220 & – & – & – & 700 & [42] \\ Rice straw & – & 490 & 13.2 & 37 & – & – & 9.54 & 500 & [37] \\ Sewage sludge & – & 470 & 64 & 7 & 56 & – & 35 & 450 & [43] \\ Sugarane bagasse & – & 710 & 17.7 & 40 & – & – & 4.34 & 500 & [37] \\ Eucalyptus wood & 7.0 & 824 & 5.7 & 144 & 0.6 & – & 0.23 & 350 & [44] \\ Oak wood & – & 759 & 1.0 & 759 & – & 1.1 & – & 350 & [38] \\ Oak wood & – & 884 & 1.2 & 737 & – & 2.2 & – & 600 & [38] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Selected properties of biochar, depending on the materials applied and the temperature of the pyrolysis process. biomass has a significant impact on the heat transfer process and product distribution. Numerous experiments in the process of pyrolysis have confirmed that carbonization product's efficiency increases at low heating rates. During fast heating, the efficiency of volatile parts increases and less secondary reactions occur [48]. In the case of reactors with a high biochar production capacity, the fixed bed reactor and fast-moving fluidized bed reactors should be considered. In the case of slow pyrolysis, the use of a fixed bed allows the use of a large working surface of the reactor. Fluidized beds allow the process to be carried out much faster but are limited by volume for technological reasons [49].