Influence of Biochar Addition on Nitrogen Transformation during Copyrolysis of Algae and Lignocellulosic Biomass.

Algae are extremely promising sustainable feedstock for fuels and chemicals, while they contain high nitrogen content, which may cause some serious nitrogen emission during algae pyrolysis utilization. In this study, we proposed a feasible method to control the nitrogen emission during algae pyrolysis by introducing lignocellulosic biomass and biochar addition. Nitrogen transformation mechanism was investigated through quantitative analysis of N-species in the pyrolysis products. Results showed that copyrolysis of algae and lignocellulosic biomass greatly increased nitrogen in solid char with large amount of NH3 and HCN releasing (∼20 wt %), while nitrogen in bio-oil decreased largely. With biochar addition, NH3, HCN, and N-containing intermediates (amines/amides and nitriles) reacted with higher active O-species (O-C═O, -OH, and -COOH) in biochar addition, and formed large amounts of amine/amide-N, pyridinic-N, pyrrolic-N, and quaternary-N on the surface of biochar addition, which led to most nitrogen being enriched in char product and biochar addition (over 75 wt %) at the expense of amines/amides, nitriles, and N-containing gas (only 3 wt % NH3 and HCN emission; decrease of 85%). These results demonstrated that biochar addition showed a positive influence on fixation of N-species during thermochemical conversion of algae and could convert nitrogen to valuable N-doped biochar materials.

Pyrolysis of Chinese chestnut shells: Effects of temperature and Fe presence on product composition.

To understand the role of Fe on biomass pyrolysis, Fe-catalyzed biomass pyrolysis in a fixed-bed reactor was investigated. It was found that the introduction of Fe increased the yields of gases and solid char while decreasing the yield of liquid oil. With increasing temperature, Hydrogen content in gaseous products obtained in the presence of Fe increased, while that of CH4 decreased. In the case of liquid oil, the introduction of Fe promoted the formation of ketones and acids at 400-600 °C, and these species became dominant (67.51%) at 700-800 °C. Finally, solid char obtained in the presence of Fe at 700-800 °C featured a larger pore volume, specific surface area, and graphitization degree, and was characterized by a mesoporous structure with narrow pores size distribution (∼5.3 nm).

Mechanism of biomass activation and ammonia modification for nitrogen-doped porous carbon materials.

The effect of chemical activation and NH3 modification on activated carbons (ACs) was explored via two contrasting bamboo pyrolysis strategies involving either two steps (activation followed by nitrogen doping in NH3 atmosphere) or one step (activation in NH3 atmosphere) with several chemical activating reagents (KOH, K2CO3, and KOH + K2CO3). The ACs produced by the two-step method showed relatively smaller specific surface areas (∼90% micropores) and lower nitrogen contents. From the one-step method, the ACs had larger pore diameters with about 90% small mesopores (2-3.5 nm). Due to a promotion effect with the KOH + K2CO3 combination, the AC attained the greatest surface area (2417 m2 g-1) and highest nitrogen content (3.89 wt%), endowing the highest capacitance (175 F g-1). The balance between surface area and nitrogen content recommends KOH + K2CO3 activation via the one-step method as the best choice for achieving both greener production process and better pore structure.

Investigation on biomass nitrogen-enriched pyrolysis: Influence of temperature.

Biomass (bamboo waste) nitrogen-enriched pyrolysis was carried out in a fixed bed with NH3 atmosphere at 400-800 °C, and formation mechanism of N-containing species was explored in depth. Results showed that N-enriched pyrolysis greatly increased bio-oil and gas yields. H2 yield increased sharply to 130 mL/g (32.93 vol%) and became the main composition at higher temperature, while CH4 and CO yields deceased, and the lower heating value of gas reached ∼14 MJ/Nm3. For bio-oil, the content of phenols (main compositions) and N-containing species increased significantly, and the maximums reached 61.33% and 11.47%, respectively. While that of acetic acid (disappeared), O-containing species (aldehydes/ketones/furans/esters) and aromatics decreased largely accordingly. For biochar, Nitrogen content increased, and it contained abundant pyridininc-N, pyrrolic-N, quaternary-N, and pyridone-N-oxide. Possible reaction pathways of biomass N-enriched pyrolysis was proposed based on products evolution. In conclusion, biomass N-enriched pyrolysis could obtain high-valued N-containing chemical species and functional biochar.

Influence of NH3 concentration on biomass nitrogen-enriched pyrolysis.

In this study, nitrogen was used to replace oxygen through biomass N-enriched pyrolysis in a fixed-bed reactor to obtain N-containing chemicals and N-doped biochar. Influence of NH3 concentration on the formation mechanism of N-species and electrochemical performance of N-doped biochar was investigated in depth. Results showed that increasing NH3 concentration promoted bio-oil and gas generation, and increased H2, CH4 and CO yield at the diminishing of CO2. Simultaneously, bio-oil showed lower oxygen content with non-methoxy phenols and N-heterocyclics as the main components, and the maximums were 57.73% and 16.21% at 80 vol% NH3 concentration, respectively. With regard to solid N-doped biochar, nitrogen content (4.85 wt%), N-containing groups and specific surface area (369.59 m2/g) increased greatly, and excellent electrochemical property (120 F/g) was shown with NH3 concentration increasing. However, NH3 conversion efficiency decreased gradually with NH3 increasing, and 40 vol% may be the optimum NH3 concentration for biomass N-enriched pyrolysis.

Co-pyrolysis of lignocellulosic biomass and microalgae: Products characteristics and interaction effect.

Co-pyrolysis of biomass has a potential to change the quality of pyrolytic bio-oil. In this work, co-pyrolysis of bamboo, a typical lignocellulosic biomass, and Nannochloropsis sp. (NS), a microalgae, was carried out in a fixed bed reactor at a range of mixing ratio of NS and bamboo, to find out whether the quality of pyrolytic bio-oil was improved. A significant improvement on bio-oil after co-pyrolysis of bamboo and NS was observed that bio-oil yield increased up to 66.63wt% (at 1:1) and the content of long-chain fatty acids in bio-oil also dramatically increased (the maximum up to 50.92% (13.57wt%) at 1:1) whereas acetic acid, O-containing species, and N-containing compounds decreased greatly. Nitrogen transformation mechanism during co-pyrolysis also was explored. Results showed that nitrogen in microalgae preferred to transform into solid char and gas phase during co-pyrolysis, while more pyrrolic-N and quaternary-N generated with diminishing protein-N and pyridinic-N in char.