Study on carbon rearrangements of CO2 co-feeding pyrolysis of corn stover and oak wood

Developing a sorptive material of cadmium from pyrolysis of hen manure

A large amount of manure is generated from concentrated animal feeding operations (CAFOs), leading to serious environmental issues and hazardous risks from pathogens, such as methicillin-resistant Staphylococcus aureus. Therefore, developing an effective method for manure disposal is essential. Thus, in this study, we suggest the use of CO2 in pyrolysis of hen manure (HM) as an effective method to convert the carbon in HM into syngas (especially carbon monoxide (CO)). HM was used and tested as the model compound. From the results of thermo-gravimetric analysis, the decarboxylation of CaCO3 in HM in the presence of N2 was realized at temperatures ranging from 638 to 754 °C. The Boudouard reaction was observed at ≥ 664 °C in the presence of CO2. Despite the lack of occurrence of the Boudouard reaction, more CO formation was observed in the presence of CO2 at ≥ 460 °C. This was deemed as a homogeneous reaction induced by CO2. Considering the high Ca content of HM, HM biochar in N2 and CO2 were used as adsorbent for removal of Cadmium (Cd), which is toxic heavy metal. The adsorption capacities of HM_N2 and HM_CO2 were 302.4 and 95.7 mg g-1, respectively. The superior performance of HM_N2 is mainly attributed to the presence of Ca(OH)2, which provides favorable (alkaline) conditions for precipitation and ion exchange. Our results indicate the environmental benefits from using CO2. Specifically, CO2 (representative greenhouse gas) converted into fuel. Given this, pyrolysis of HM in the presence of CO2 was achieved at ≤ 640 °C, and the atmospheric condition should be switched from CO2 to N2 at ≥ 640 °C to ensure the decarboxylation of CaCO3.

Sustainable valorization of styrofoam and CO2 into syngas

Plastic is a versatile material broadly used in a variety of industries. However, the current disposal practices for plastic wastes (incineration/landfilling) add the hazardous materials into the environment. To offer a sustainable valorization platform for plastic waste, this study adopted the catalytic pyrolysis process using CO₂ as a co-feedstock. A model plastic waste collected from a seaport was waste buoy (WB), which has been widely used in fishing industry. Prior to the pyrolysis tests, the exact type of plastic in WB and the thermolytic characteristics of WB were examined. Since the WB was made of polystyrene, it was mainly converted into styrene monomer (styrene), dimer (diphenyl-1-butene), and trimer (2,4,6-triphenyl-1-hexene) from pyrolysis of WB. To further valorize/detoxify styrene derivatives into value-added syngas, catalytic pyrolysis of WB was practiced using the Ni-based catalysts (2/5/10 wt% Ni/SiO₂). The yield of H₂ from the catalytic pyrolysis process of WB was more than one magnitude higher comparing to that from the non-catalytic one. H₂ formation also increased as catalyst loading increased. When flow gas was switched from inert gas to CO₂, CO gas formation was enhanced due to the chemical reactions between CO₂ and styrene derivatives over Ni catalysts. Syngas (H₂/CO) formation under the CO₂ condition was 5 times higher in comparison to the N₂ condition in catalytic pyrolyses of WB with 10 wt% Ni/SiO₂. CO₂ also effectively suppressed coke deposition on a Ni catalyst. This study proposes a sustainable valorization and disposal platform for used plastic waste and greenhouse gas (CO₂), converting them into value-added fuel.

Functionalizing biochar by Co-pyrolysis shaddock peel with red mud for removing acid orange 7 from water

Biochar modification by metal/metal oxide is promising for improving its adsorption capability for contaminants, especially the anions. However, conventional chemical modifications are complicated and costly. In this study, novel Fe/Fe oxide loaded biochars (RMBCs) were synthesized from a one-step co-pyrolysis of red mud (RM) and shaddock peel (SP), and their potential application for removing anionic azo dye (acid orange 7, AO7) from the aqueous environment was evaluated. Fe from red mud was successfully loaded onto biochars pyrolyzed at 300-800 °C, which presented from oxidation form (Fe₂O₃) to the reduction forms (FeO and Fe⁰) with increasing pyrolysis temperature. The RMBC produced at 800 °C with RM:SP mass ratio of 1:1 (RMBC800_1:1) exhibited the best capability for AO7 removal (∼32 mg/g), attributed to both adsorption and degradation. The higher surface area of RMBC800_1:1 and its greater affinity for AO7 led to the higher adsorption. In addition, RMBC800_1:1-induced degradation of AO7 was another key mechanism for AO7 removal. The reduction forms of Fe (FeO or Fe⁰) in RMBC800_1:1 may provide electrons for breaking down the azo bond in AO7 molecules and result in degradation, which is further enhanced in acid conditions due to the participation of readily release of Fe²⁺ and the available H⁺ in AO7 degradation. Furthermore, RMBC800_1:1 can be easily separated from the treated water by using magnetic field, which significantly benefits its separation in wastewater treatment.

Removal of Inorganic Salts in Municipal Solid Waste Incineration Fly Ash Using a Washing Ejector and Its Application for CO2 Capture

This study investigated the effects of washing equipment for inorganic salts, such as NaCl, KCl, and CaClOH, to decontaminate municipal solid waste incineration fly ash (MSW-IFA). Based on the feature of hydrodynamic cavitation, the device developed in this study (referred to as a ‘washing ejector’) utilizes the cavitation bubbles. A washing ejector was analyzed under a range of conditions, employing as little water as possible. In hydrodynamic cavitation, the increase in fluid pressure with increasing static pressure is mainly attributed to the increase in particle–bubble collisions via the cavitation flow. The results revealed that the fluid pressure influenced the removal of inorganic salts during cavitation in water. This is because during the washing process from the collapse of cavitation bubbles, the release is achieved through the dissolution of inorganic salts weakly bound to the surface. After treatment by a washing ejector, the removal of soluble salts elements such as Cl, Na, and K was reduced by approximately 90%. Removing the inorganic salts in the IFA altered the characteristics of the Ca-related phase, and amorphous CaCO₃ was formed as the cavitation flow reacted with CO₂ in the ambient air. Furthermore, the washing effluent produced by washing IFA was found to be beneficial for CO₂ capture. The washing effluent was enriched with dissolved Ca from the IFA, and the initial pH was the most favorable condition for the formation of CaCO₃; thus, the effluent was sufficient for use as a CO₂ sequestration medium and substitute for the reuse of water. Overall, the process presented herein could be effective for removing soluble salts from IFA, and this process is conducive to utilizing IFA as a resource.

Removal of phosphate from water by paper mill sludge biochar

Biochar modification by metals and metal oxides is considered a practical approach for enhancing the adsorption capacity of anionic compounds such as phosphate (P). This study obtained paper mill sludge (PMS) biochar (PMSB) via a one-step process by pyrolyzing PMS waste containing ferric salt to remove anionic P from water. The ferric salt in the sludge was transformed into ferric oxide and zero-valent-iron (Fe⁰) in N₂ atmosphere at pyrolysis temperatures ranging from 300 to 800 °C. The maximum adsorption (Q_m) of the PMSBs for P ranged from 9.75 to 25.19 mg P/g. Adsorption is a spontaneous and endothermic process, which implies chemisorption. PMSB obtained at 800 °C (PMSB800) exhibited the best performance for P removal. Fe⁰ in PMSB800 plays a vital role in P removal via adsorption and coprecipitation, such as forming the ≡Fe-O-P ternary complex. Furthermore, the possible chemical precipitation of P by CaO decomposed from calcite (CaCO₃; an additive of paper production that remains in PMS) may also contribute to the removal of P by PMSB800. Moreover, PMSBs can be easily separated magnetically from water after application and adsorption. This study achieved a waste-to-wealth strategy by turning waste PMS into a metal/metal oxide-embedded biochar with excellent P removal capability and simple magnetic separation properties via a one-step pyrolysis process.

Strategic disposal of flood debris via CO2-assisted catalytic pyrolysis

Recent abnormal climate changes resulted in the dramatic alternation of rainfall and flood patterns in many countries. The massive generation of flood debris, a mixture of soil (sediment), biomass, plastic, metal, and various hazardous materials, poses various environmental and public health problems. This study suggests a sustainable technical platform to convert the hazardous materials into value-added products. CO₂-assisted pyrolysis was used to thermally convert flood debris into syngas (H₂ and CO). CO₂ enhanced the syngas production due to gas phase homogeneous reactions (HRs) between CO₂ and volatile hydrocarbons evolved from pyrolysis of flood debris. For improvement of HRs in line with enhancement of syngas production, additional thermal energy and earth abundant catalyst were used. In particular, Ni/SiO₂ catalyst increased more than one order of magnitude higher syngas production, comparing to non-catalytic pyrolysis. Synergistic effect of CO₂ and Ni catalyst showed nearly 50% more production of syngas in reference to catalytic pyrolysis under N₂. During flood debris pyrolysis, compositional matrix of flood debris was also determined by detecting index chemicals of waste materials that cannot be identified by naked eyes. Thus, this study confirmed that CO₂-assisted pyrolysis is a useful tool for conversion of flood debris into value-added chemicals.