Evolution of Inherent Oxygen in Solid Fuels during Pyrolysis

ACS Sustainable Chem. Eng.

et al. 2020

Antibiotic fermentation residues (AR) are a potential biohazard to the environment and human health. Pyrolysis is an effective method that can be utilized to decompose residual antibiotics and convert AR into valuable products such as biofuels (bio-oils), biochars, and pyrolysis gas. The nitrogen element in AR affects the utilization of the products significantly. Clarifying the product characteristics and nitrogen migration mechanism of AR during pyrolysis will be helpful for the resource utilization of AR. In this study, pyrolysis experiments of penicillin fermentation residue (PR) were conducted at 400−700 °C. The cyclization of nitrogen from the protein/amino acids in PR facilitated the generation of pyrrole and pyridine. During this process, NH 3 , HCN, and HNCO were released into pyrolysis gas. When heated to 600−700 °C, the pyridine and pyrrole in the biochars produced quaternary nitrogen groups through condensation and generated HCN through secondary thermal cracking at the same time. The total content of nitrogen compounds in the bio-oil reached a maximum at 400 °C (57.3%). Amide, amine, pyridine, and indole were the principal nitrogenous species. Additionally, dipeptides and 2,5-piperazinedione (DKP) compounds, the important intermediates in protein/amino acid pyrolysis, were also found in the bio-oil. The formation and transformation processes of the main N-containing compounds in the bio-oil were analyzed using quantum chemical calculations. The reaction barrier and reaction energy of every reaction step were evaluated to determine the most energetically favorable reaction paths. The three most abundant amino acids in PR were used as model molecules for calculating the formation process of DKP. In addition, the results of the quantum chemical calculations indicated that DKP could decompose into nitriles, amides, and amines. Moreover, the formation and decomposition of pyridine, the decomposition of uracil, and the formation of indole were also analyzed by quantum chemical calculations.

Section: Resultsmentioning

confidence: 97%

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Nitrogen Migration Mechanism during Pyrolysis of Penicillin Fermentation Residue Based on Product Characteristics and Quantum Chemical Analysis

Hong

ACS Sustainable Chem. Eng.

et al. 2020

“…X‐ray photoelectron spectroscopy (XPS) analysis (Table ) reveals that sample Fd‐AC contains less surface O content than sample AC, which results from the more efficient activation in Fd‐AC by vacuum freeze‐drying. Because high‐temperature annealing is an effective method to eliminate oxygen atoms, sample Fd‐AC‐a has the least surface O content. The low oxygen content is of great benefit to enhance the EDLC life span of Fd‐AC‐a at voltages over 2.5 V.…”

Section: Resultsmentioning

confidence: 99%

Humic acid‐derived hierarchical porous carbon preparation using vacuum freeze‐drying for electric double layer capacitors

Jia

Chang

et al. 2018

J Chinese Chemical Soc

Electric double layer capacitors (EDLCs) preserve charge by reversible physisorption of electrolyte ions on the surface of porous active materials. Therefore, engineering a reasonable pore structure and reducing oxygen‐containing groups of carbon materials are efficient approaches to enable rapid ion diffusion pathways and long life span, respectively. Here, humic acid (HA)‐derived hierarchical porous carbon was fabricated by vacuum freeze‐drying, KOH activation, and subsequent annealing. The macropores were generated from the vacancies where the ice crystals in the HA–KOH gels initially occupied during vacuum‐freeze drying, while abundant micropores were created from homogeneous KOH activation. In addition, subsequent annealing further reduced the oxygen‐containing groups. When used as EDLC electrodes in 1 mol/L TEABF4/PC organic electrolyte, they could give a high capacitance of 150 F/g at 0.05 A/g and excellent rate performance of 81% (with capacitance of 121.46 F/g at 10 A/g). More importantly, the hierarchical porous carbon displays superior capacity retention of 85.6% after 10,000 cycles at 1 A/g at 2.7 V.

“…52,66 On the contrary, the relative contents of C−O groups after LZ pyrolysis was found out to increase from 11.9% to 21.24%, mainly due to their formation through both elimination of the hydroxyl groups 65 as well as the breakage of CO groups. 67 Meanwhile, after LZ pyrolysis, more COOH groups were formed through the further conversion of the formed C−O groups, 68,69 though COOH groups were reported as thermally unstable 70 and easily decomposed through decarboxylation reaction to form H 2 O and CO 2 , as discussed in Section 3.4 above.…”

Section: Energy and Fuelsmentioning

confidence: 99%

Effect of Reaction Temperature on the Chemical Looping Combustion of Coal with CuFe₂O₄ Combined Oxygen Carrier

et al. 2017

Energy Fuels

Reaction temperature is regarded as one of the important factors influencing the efficient utilization of coal in chemical looping combustion (CLC), but research into its effect on the chemical structure of coal in CLC is limited. In the research reported herein, the oxygen-transfer mechanism of CuFe2O4 prepared through the sol–gel method combined with combustion synthesis, along with the characteristics of its reaction with a typical coal of high sulfur and high ash contents (abbreviated as LZ), were systematically investigated at different final reaction temperatures, with the research focused on the effect of reaction temperature. H2-temperature-programmed reduction of CuFe2O4 indicated that the first reduction of the Cu2+ ion in CuFe2O4 was advantageous in the later transmission of atomic oxygen from the Fe3+ reduction, while temperature-programmed decomposition of CuFe2O4 under a N2 atmosphere validated the potential of CuFe2O4 to emit O2 through its direct decomposition. Furthermore, thermogravimetric analysis and Fourier transform infrared spectroscopy showed better reaction performance between CuFe2O4 and LZ coal than other ferrite oxygen carrier (OC) candidates, such as MnFe2O4, NiFe2O4, and CoFe2O4, which we studied previously. Comprehensive characterization of the solid products from reaction of CuFe2O4 with LZ coal by field emission scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy (XPS) indicated that CuFe2O4 was mainly reduced to Cu and Fe3O4. At the same time, some oxygen-deficient CuFe2O4 was also formed through disintegration of the original CuFe2O4 spinel with more Cu2+ and Fe3+ ions occupying the octahedral sites, which benefited the transmission of the atomic oxygen involved in the CuFe2O4. Finally, XPS analysis of the LZ coal residue after its reaction with CuFe2O4 indicated that the main obstacle to fully utilizing LZ coal at the molecular scale in CLC was the dominance of C–C/C–H groups, with the highest relative content over 62% at the 700 °C reaction temperature. Increasing the reaction temperature was quite effective to promote the efficient utilization of LZ coal from the molecular perspective during the reaction between LZ coal and CuFe2O4.