Search

Renewable source-derived carbon is found to be a green alternative catalyst to zeolite for the pyrolysis of plastics. However, only polyethylene (PE) catalytic pyrolysis over biomass-derived carbon has been extensively studied. In this work, carbon was produced from industrial organic solid waste using different activation agents, and their catalytic performance on the thermal degradation of typical polymers, namely PE, polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET) were investigated. The degradation mechanisms and the roles of different active sites of the carbons are discussed. Steam failed to activate the carbon, which has a low specific surface area (6.7 m2/g). Chemical activation using H3PO4 and ZnCl2 produces carbons with higher specific surface area and more porosity. The pyrolysis characteristics of LDPE, PP, PS, and PET catalyzed by the carbons were studied using TGA and a fixed-bed reactor. The thermogravimetric results indicate that all three carbons reduce the pyrolysis temperature. The analysis of the products shows that the P- and Zn-involved acid sites on the AC-HP and AC-ZN change the reaction pathway of plastics and promote: (1) C-C cracking and aromatization of polyolefins; (2) the protonation of phenyl carbon of PS to yield higher benzene, toluene, and ethylbenzene; and (3) the decarboxylation of the terephthalic acid intermediate of PET, resulting in higher CO2 and benzene. In addition, the high-value chemicals, long-chain alkylbenzenes, were found in the liquids of AC-ZN and AC-HP. The long-chain alkylbenzenes are probably formed by acid-catalyzed alkylation of aromatic hydrocarbons. This study provides basic data for the development of a cheap catalyst for plastic pyrolysis.

Hydrogen-rich gas production from catalytic steam gasification of coal was investigated in the presence of iron ore in a vertical fixed bed reactor. The addition of iron ore significantly promoted the H2 yields. The effects of operation parameters (upper zone temperature, lower zone temperature, steam concentration, and iron to coal ratio) on the yield of selected gaseous products (H2 and CO) during catalytic steam gasification, were studied using Taguchi method. The results of signal-to-noise ratio indicated that steam concentration and iron to coal ratio were the most important parameters in determining the yield of H2 and CO, respectively. Semi-quantification X-ray diffraction analysis of iron ores indicated that increase in steam concentration intensified the oxidization of low valence iron compounds to Fe3O4. In addition, formation of Fe3O4 was also favored with increasing reaction temperatures (600 °C–900 °C). However, the formation of Fe3O4 was inhibited at higher reaction temperature (1000 °C) due to the destruction of porous structures of the iron ore.

The economic feasibility of a facility producing jet fuel range cycloalkanes, hydrogen and biochar via microwave-assisted catalytic pyrolysis integrated with mild hydrogenation was evaluated by modeling a 1000 metric dry tonne feedstock/day using ASPEN PLUS®. The effects of hydrogenation solvent, heat integration, and coproducing H2 or syngas were investigated in different analysis scenarios. The results indicated that the production of jet fuel could reach 47882.74 Gallon/day, with 9.58 Metric tonne/day biochar and 28200 kg/day H2 as coproducts. The lowest minimum selling price of 3.78 $/Gallon was obtained when using n-hexane as the hydrogenation solvent and coproducing H2 with heat integration. The sale of H2 offset the high production cost, resulting in a significant decrease in the minimum selling price. Sensitivity analysis indicated that the production process was greatly sensitive to total capital investment, internal rate of return, market prices of feedstock and H2.

The catalytic conversion of Douglas fir sawdust into bio-phenols on activated carbons (AC) obtained by chemical activation of corn stover with H3PO4 was investigated. Taguchi experimental design was used to optimize the preparation of AC using microwave assisted pyrolysis. Based on an overall consideration of AC yield, bio-oil yield, and phenols content, the optimized conditions were phosphoric acid to biomass ratio of 0.8, microwave power of 600 W and reaction time of 20 min. The bio-oils were rich in phenolic compounds (up to 90 area %) that mainly comprised phenol, methyl and ethyl phenol. During the catalytic pyrolysis of biomass with AC, phenolic compounds could either be derived from decomposition of lignin, followed by deoxygenation, or derived from furfurals, which were degradation products of carbohydrates. The catalytic activities of ACs were mainly owing to the well-developed porosity and abundant acidic surface functional groups. The porous structures of ACs were characterized by N2 isotherms, showing a strong dependence on the acid impregnation ratio and microwave irradiation power. The presence of acidic phosphoric-containing surface functional groups was confirmed by SEM/EDX, FTIR and NH3-TPD.

Weight loss and gas release behavior of mengdong coal (MD) during pyrolysis was investigated using thermogravimetric analyzer coupled with Fourier transform infrared spectroscopy (TGA-FTIR), and char evolution of coal chars derived at different pyrolysis temperature were analyzed with two dimensional perturbation correlation infrared spectroscopy (2D-PCIS) method to reveal the mechanism of mengdong coal pyrolysis. The MD coal showed a significant weight loss at 300– 600 °C during pyrolysis. Free OH groups reacted before OH-πand self-associated n-mers hydrogen bond. The demethylenation reaction sequence was aliphatic R3-CH groups and asymmetric aliphatic R-CH3 > symmetric aliphatic R2-CH2 > asymmetric aliphatic R2-CH2. CO2 releasing mainly resulted from the crack of C O in aryl ethers groups, C O in alcohols in coal molecular. The effect of K2CO3 on char structure was also studied. The results showed that, inherent mineral of coal presented stronger catalytic effects towards pyrolysis. K2CO3 addition influenced the reaction sequences of R3-CH, symmetric R2-CH2 and asymmetric R2-CH2 insignificantly, but could significantly change the correlation of C O, C O, CH CH3, and aromatic C C bond.

Chars from wastes/biomass pyrolysis are widely used as catalysts. But their catalytic mechanism is not clear enough. To explore the role of inorganics in char-based catalysts, in this research, chars from municipal solid wastes (MSW) and wheat straw (WS) were compared for their catalytic performances and structure changes in reforming volatiles from MSW and WS pyrolysis. Results showed that MSW char (ash: 43 wt%) was more active than WS char (ash: 16 wt%) in reforming both volatiles within 500–700 °C, which facilitated higher syngas yield. 74% of the metals existed as non-evaporable acid-soluble inorganics in MSW char, which favored the transformation of microcrystalline carbon into amorphous carbon by carbon gasification yet increased aromaticity of its carbon matrix; while 27% of metals in WS char were organically bound alkali and alkaline-earth metals (AAEMs), and aromaticity of its carbon lattice increased from 0.39 to 0.67 with increase in reforming temperature. Additionally, WS char was characterized with larger aromatic ring size after reforming temperatures. Rich acid-soluble inorganics in MSW char were found to be favorable to its high activity; while migration of AAEMs caused the lower activity of WS char. These findings will help to improve catalytic activity of char-based catalysts.

The purpose of this study was to utilize gasification derived char as a catalyst support for tar removal. Red cedar char collected from downdraft bed gasification was chemically activated into activated carbon and impregnated with nickel acetate and nickel nitrate. The effects of nickel salts precursor, nitric acid treatment of support and reduction of nickel in hydrazine medium on catalyst performance were studied. It was found nickel nitrate was a better nickel precursor than nickel acetate for preparation of char supported nickel catalyst. The catalyst impregnated with nickel nitrate was found more active in steam reforming of toluene than the catalyst impregnated with nickel acetate. TEM results indicated that nickel particle size of the catalyst impregnated with nickel nitrate was much smaller than that of the catalyst impregnated with nickel acetate. Toluene showed higher removal efficiency than naphthalene. The presence of naphthalene decreased the toluene removal.

Tar removal is one of the major challenges in implementation of biomass gasification technology. Syngas tars causes formation of aerosols and soots, which plug filters, reactors and fuel lines. In this study, a char-derived catalyst was tested in removal of tar produced from pyrolysis of kraft lignin in a pyroprobe reactor. The effects of reaction temperature (700, 800 and 900 °C), water amount (5–10 μl), pressure (0.1–2.2 MPa) and atmosphere (inert and hydrogen) on catalytic conditioning of tar components were assessed. The tar components were analyzed by GC/MS. Catechols were the most abundant tar components followed with phenols and guaiacols during non-catalytic kraft lignin pyrolysis. Results indicated that the char-based catalyst effectively decreased the contents of lignin tar. Reaction temperature, water loading and reaction pressure significantly affected the tar removal. An increase in reaction temperature led to an increase in removal efficiency of most tar components except naphthalene. Excessive water loading (10 μl) decreased the tar removal efficiency of char-based catalyst. High pressure promoted the catalytic conversion of lignin tar. Tar contents decreased significantly when hydrogen was used as a reaction medium and thus promoted the conversion of lignin into non-condensable gas.

Downdraft gasification of forage sorghum and red cedar wood was studied with the aim of determining the characteristics of produced char for its further application, such as soil amendment, sorbent and solid fuel. Ultimate, proximate, XRD and NMR were used to investigate physical and chemical properties of char and thermo-analytic methods were used to determine kinetics of char gasification. The NMR results showed that red cedar and sorghum chars both contain aromatic carbon, but aliphatic carbon and o-alkyl carbon are more evident in the red cedar char than in the sorghum char. Char derived from downdraft gasification had higher heating values and lower ash contents than char derived from fluidized bed gasification, indicating char derived from downdraft gasification is more suitable for applications, such as soil amendment, than char from fluidized bed gasification. Micropores and mesopores were found in both red cedar and sorghum chars. The gasification reactivity of red cedar char was higher than that of sorghum char. Activation energies were found to be 163 and 167 kJ/mol based on shrinking core model and 147 and143 kJ/mol based on random pore model for sorghum char and red cedar char, respectively.