Nana Peng

Co-liquefaction of microalgae and lignocellulosic biomass in subcritical water

This study investigated co-liquefaction of microalgae (Chlorella pyrenoidosa, CP) and lignocellulosic biomass (Rice husk, RH) in subcritical water for bio-oil production. The effects of liquefaction temperature (200-350°C), residence time (10-90min), solid concentration (10-30wt.%) and mass ratio of CP/RH on product distribution were investigated. The results showed that the highest yield of bio-crude oils at the combination of 50% CP with 50% RH was obtained at 300°C temperature, 60min residence time and 20wt.% solid concentration. The oil yields increased gradually with the increased mass ratio of CP/RH. The major compounds identified in bio-crude oils from hydrothermal liquefaction (HTL) of RH were cyclic oxygenates (20.62%), followed by esters, ketones and alcohols (17.19%). As for CP, the main components were straight & branched amides (28.38%). A synergistic interaction was observed between CP and RH during co-liquefaction, resulting in decreased acidity and nitrogen content of bio-crude oils.

Combustion behavior and kinetics of low-lipid microalgae via thermogravimetric analysis

Thermogravimetric analysis and differential thermal analysis were employed to investigate combustion characteristics of two low-lipid microalgae, Chlorella pyrenoidosa (CP) and Spirulina platensis (SP) and iso-conversional Starink approach was used to calculate the kinetic parameters in the present study. The results showed that three stages of mass loss, including dehydration, devolatilization and char oxidation, were observed during combustion of both of two low-lipid microalgae. The whole weight loss of combustion of two microalgae was both shifted to higher temperature zones with increased heating rates from 10 to 40 K/min. In the 0.1-0.9 conversion range, the apparent activation energy of CP increased first from 51.96 to 79.53 kJ/mol, then decreased to 55.59 kJ/mol. Finally, it slightly increased to 67.27 kJ/mol. In the case of SP, the apparent activation energy gradually increased from 68.51 to 91.06 kJ/mol.

Emission, distribution and toxicity of polycyclic aromatic hydrocarbons (PAHs) during municipal solid waste (MSW) and coal co-combustion.

Emission and distribution characteristics of polycyclic aromatic hydrocarbons (PAHs) were investigated during municipal solid waste (MSW) and coal combustion alone and MSW/coal blend (MSW weight fraction of 25%) co-combustion within a temperature range of 500°C-900°C. The results showed that for all combustion experiments, flue gas occupied the highest proportion of total PAHs and fly ash contained more high-ring PAHs. Moreover, the 3- and 4-ring PAHs accounted for the majority of total PAHs and Ant or Phe had the highest concentrations. Compared to coal, MSW combustion generated high levels of total PAHs with the range of 111.28μg/g-10,047.22μg/g and had high toxicity equivalent value (TEQ). MSW/coal co-combustion generated the smallest amounts of total PAHs and had the lowest TEQ than MSW and coal combustion alone. Significant synergistic interactions occurred between MSW and coal during co-combustion and the interactions suppressed the formation of PAHs, especially hazardous high-ring PAHs and decreased the TEQ. The present study indicated that the reduction of the yield and toxicity of PAHs can be achieved by co-combustion of MSW and coal.

Effect of hydrothermal carbonization on migration and environmental risk of heavy metals in sewage sludge during pyrolysis

The heavy metals distribution during hydrothermal carbonization (HTC) of sewage sludge, and pyrolysis of the resultant hydrochar was investigated and compared with raw sludge pyrolysis. The results showed that HTC reduced exchangeable/acid-soluble and reducible fraction of heavy metals and lowered the potential risk of heavy metals in sewage sludge. The pyrolysis favored the transformation of extracted/mobile fraction of heavy metals to residual form especially at high temperature, immobilizing heavy metals in the chars. Compared to the chars from raw sludge pyrolysis, the chars derived from hydrochar pyrolysis was more alkaline and had lower risk and less leachable heavy metals, indicating that pyrolysis imposed more positive effect on immobilization of heavy metals for the hydrochar than for sewage sludge. The present study demonstrated that HTC is a promising pretreatment prior to pyrolysis from the perspective of immobilization of heavy metals in sewage sludge.

N-Doped biochar derived from co-hydrothermal carbonization of rice husk and Chlorella pyrenoidosa for enhancing copper ion adsorption

Biochar derived from rice husk was modified by microalgae Chlorella pyrenoidosa as a natural nitrogen-rich precursor in a hydrothermal environment for copper ion (Cu(II)) adsorption. Pristine biochar derived from hydrothermal carbonization of individual rice husks was included as a control. FTIR, SEM and BET analyses indicated that the modified biochar is more hydrophobic and basic than the pristine biochar due to the anchoring of surface nitrogenous functionalities. The adsorption of copper ions onto the pristine and modified biochar was investigated with respect to pH, adsorbent dosage, contact time, temperature, kinetics and isotherms. The results showed that modification of the biochar by nitrogen significantly increased the copper adsorption capacity from 13.12 mg g−1 for the pristine biochar to 29.11 mg g−1 for the modified biochar. Adsorption of copper ions by the modified biochar was dominated by surface complexation rather than through the electrostatic attractions that dominated adsorption for the pristine biochar.

Hydrochar supported bimetallic Ni–Fe nanocatalysts with tailored composition, size and shape for improved biomass steam reforming performance

Multicomponent nickel–iron alloy nanoparticles supported on hydrochar were synthesized by a facile one-step hydrothermal strategy. Spinel nickel ferrite (NiFe2O4) with a small crystalline size around 10 nm was uniformly dispersed on a bimetallic catalyst. The roles of the Ni/Fe doping concentration and calcination temperature in tailoring the phase, morphology and size of the Ni–Fe alloy nanoparticles were investigated. To probe the catalytic abilities of the prepared bimetallic catalysts, a two-stage reaction system was applied for steam gasification of sewage sludge. Compared to monometallic nickel nanoparticles, the synthesized bimetallic catalyst, especially Ni0.25Fe0.25/HC calcined at 700 °C, showed excellent dispersibility of the Ni–Fe alloy NPs and exhibited a strong metal–support interaction, which allowed for better suppression of carbon deposition and nanoparticle agglomeration in the reforming process. The best catalytic performance resulted in a promoted hydrogen selectivity of 113.7 g H2 per kg sludge with a low tar yield of 2.3 mg g−1 under mild gasification conditions. These shape- and size-modulated nanocatalysts harbor promising potential for their application as a highly efficient catalyst for hydrogen production via steam gasification of sewage sludge.