Variation behavior of organic compounds in melamine-urea-formaldehyde impregnated bond paper in different pyrolysis stages

Melamine-urea-formaldehyde impregnated bond paper (MUF) is widely used as panel coating and decorative raw paper. Inappropriate treatment of MUF may lead to environmental pollution. In this study, routine MUF and MUF treated with additional titanium (MUF-T) were subjected to fast pyrolysis, and the product properties at different temperatures were investigated. The pyrolysis temperature was selected considering the reaction stages determined by Gaussian curve-fitting on thermogravimetric analysis curves. It was found that the presence of additional titanium changed the decomposition order of the organic components at 220 °C. Urea-formaldehyde in MUF could be decomposed at 220 °C, which had little effect on other components (melamine and cellulose). However, in terms of MUF-T, the decomposition temperature of urea-formaldehyde was postponed to 244 °C, which means that the pyrolysis strategy needs to choose a temperature higher than 244 °C. The volatiles in MUF-T are more easily converted to bio-gas or bio-oil than those in MUF. However, only CH₄ was observed in the bio-gas generated of MUF-T at 220 °C, indicating that titanium did not catalyze the fracture of oxygen-containing functional groups at low temperatures. Titanium condensed at 550 °C, and the utilization of bio-char may face a problem of titanium particle shedding.

Torrefied herb residues in nitrogen, air and oxygen atmosphere: Thermal decomposition behavior and pyrolytic products characters

The thermal decomposition behavior and pyrolytic products characters of herb residue (HR) torrefied in N₂, air and O₂ were investigated in present work. The clear gradual regularity of samples in Van Krevelen diagram exhibited the severity and some similarities of torrefaction. The activation energy (E) calculated by distributed activation energy model (DAEM) found that the E values of torrefied samples was higher than raw HR if the conversion is below 0.8. Torrefaction treatment would beneficial to increase the yield of gas but inhibit the formation of oil, and the compounds of gas and bio-oil under different torrefaction conditions are also quite different. It should be noticed that the presence of oxygen in the torrefaction atmosphere would reduce the torrefaction temperature significantly, while maintaining the severity of torrefaction and pyrolytic products distribution.

Effect of high heating rates on products distribution and sulfur transformation during the pyrolysis of waste tires

Fast pyrolysis offers a promising efficient way for the resourceful disposal of waste tires and heating rate was a key influence factor on products properties. However, the heating rates of the widely used experimental apparatus (like thermogravimetric) were generally outside the scope of most fast pyrolysis devices. To better guide actual pyrolysis process, the present study focused on the effects of high heating rates (ranged from 60 to 6000 °C/min) on products distribution and sulfur transformation during waste tires pyrolysis. And experiments were conducted at temperatures from 425 °C to 575 °C by using a self-designed photothermal reactor. The results showed that increasing heating rates posed slight effect on the products yields at 425 °C while obviously decreased char yield by forming more gases at higher temperatures. Moreover, high heating rates promoted the fast cracking of tires to form more radical fragments, leading to the formation of numerous small-molecule H₂, CH₄ and H₂S. Meanwhile, secondary reactions among nascent volatiles remarkably increased the fraction or aromatic compounds in the pyrolytic tar especially at 500 °C and 575 °C. Although high heating rates hardly changed the carbon distribution characteristics in the char, increasing heating rate from 60 to 600 °C/min significantly reduced sulfur content in the char, regardless of the final pyrolysis temperature. These findings were believed to well support the application of fast pyrolysis technique for the disposal of waste tires.

Effects of reaction conditions on products and elements distribution via hydrothermal liquefaction of duckweed for wastewater treatment

Wastewater treatment by duckweed is a naturally sustainable technology. However, its development is limited due to the lack of a follow-up treatment of duckweed. The duckweed was proposed for the treatment of rural domestic wastewater and agricultural wastewater, and it was further processed to produce bio-oil via hydrothermal liquefaction at various temperatures (250 °C-370 °C) and residence times (15-60 min). The highest bio-oil yield of 35.6 wt% was obtained at 370 °C, 45 min. The higher heating value of bio-oil was 40.85 MJ/kg, and the H/C ratio (1.72-1.98) was similar to that of petroleum (1.84). The gas chromatography-mass spectrometry analysis results revealed that the bio-oil mainly consisted of N-heterocycles, cyclic ketones, esters, amides, long-chain hydrocarbons, phenols, and aromatic intermediates. Valuable compounds (3-pyridinol, 2-pyrrolidinone, and its analogues) of high concentration were identified in the water-soluble organic matter. Compared with other materials, this study produced higher-quality bio-oil and water-soluble organic matter.

Influence of humic acids on fungal laccase-initiated 17α-ethynylestradiol oligomerization: Transformation kinetics and products distribution

Fungal laccase has aroused great concern in rapidly removing estrogens because of its ability to accelerate humification and oligomerization. Here, the effect of two humic acids (HAs) on the reaction kinetics and products distribution of 17α-ethynylestradiol (EE2) in laccase-initiated humification and coupling was systematically elucidated. Laccase from Trametes versicolor exhibited over 98.3% removal rate for EE2 at pH 5.0 within 120 min, while HAs invariably restrained EE2 transformation by competing with target-substrate for the enzymatic catalytic center. EE2 removal followed pseudo-first-order kinetics, and the rate constant was decreased markedly with increasing concentration of two HAs (0-60 mg L^-1). Additionally, laccase heightened the aromaticity and humification degrees (A_{250 nm}/A_{365 nm} ratio) of HAs probably due to the formation of new humic polymers such as (HA)_m and/or (HA)_m-(EE2)_n (m and n represent the number of HA and EE2 units, respectively). Three major EE2 oligomers were identified, in accordance with a mechanism involving the phenoxy radical-driven polymerization to yield a wide variety of self-coupling products. Notably, HAs diminished the extent of EE2 self-coupling but aggrandized the cross-coupling between EE2 and HAs, and the inhibition degree of EE2 self-coupling increased with the concentration of HAs. One major reason is EE2 could be covalently incorporated into humic molecules to produce (HA)_m-(EE2)_n cross-coupling products via radical-caused C-C, C-O-C, and/or C-O-C bonds, thereby reducing EE2 self-oligomerization. These findings highlight that HAs play a vital role in the fungal laccase-induced humification and oligomerization of EE2, which obviously alter the geochemical fate and transport of EE2 in natural aquatic ecosystems.

Effects of pyrolysis temperature and addition proportions of corncob on the distribution of products and potential energy recovery during the preparation of sludge activated carbon

The potential energy recovery during sludge activated carbon (SAC) preparation by co-pyrolysis of sewage sludge and biomass has recently gained significant attention. This study firstly evaluated the distribution of pyrolysis products including SAC, oils and gases during sludge pyrolysis at different temperatures (400 °C-800 °C) and corncob addition proportions (0-50%, w/w). The results demonstrated that with the increase of pyrolysis temperature, yield of SAC declined dramatically, while yields of pyrolysis oils and gases increased. With increasing addition of corncob, the yields of SAC and pyrolysis oils declined slightly, while the yield of gases generally increased. Then, the potential energy recovery during sludge pyrolysis was calculated, and the highest energy recovery value was 10.21 kJ/g achieved at 800 °C and 50% corncob addition. However, higher pyrolysis temperature over 600 °C resulted in lower yield and iodine adsorption capacity of SAC. Therefore, the suitable conditions were suggested to be at 600 °C with 50% corncob addition considering both adsorption performance of SAC and potential energy recovery efficiency.

Effect of inherent minerals on sewage sludge pyrolysis: Product characteristics, kinetics and thermodynamics

Inherent minerals in sludge influence sludge pyrolysis behaviors and the final products. In this study, the effects of inherent minerals on sewage sludge pyrolysis were systematically investigated by studying the pyrolysis behaviors of raw sewage sludge (RS) and HCl-washed sludge (WS), and in combination with thermodynamic equilibrium simulations for the hypothetical mineral-free sludge (AS) assumed. The pyrolysis of RS and WS was performed with a novel online thermogravimetric analyzer equipped with an infrared spectrometer and a gas chromatograph coupled with a mass spectrometer (TG-IR-GC/MS). It was found that inherent minerals influenced both the release of volatile products as a function of pyrolysis temperature, and the development of the physicochemical properties of the derived char. In the temperature range of 300-500 °C, hydrocarbons with more than 4 carbon atoms as well as aromatic compounds showed an increased release during WS pyrolysis, with respect to RS, while hydrocarbons with less than 3 carbon atoms such as CH₄ and C₃H₆ exhibited a decreased release. In addition, the inherent minerals enhanced the release of HCN and NH₃, both leading to increased NO₂ release, and the release of H₂S and COS was also promoted while the release of CH₃SH, SO₂ and CS₂ was mitigated. Kinetic analysis confirmed that a catalytic effect induced by the inherent minerals decreased the activation energy at 300-500 °C. Thermodynamic simulations suggested that inherent minerals influenced sludge pyrolysis and the derived products formation by increasing the total Gibbs energy of the sludge pyrolysis system. Therefore, considerations of sludge inherent minerals should be taken into account during pyrolysis for the purpose of value-added commodity production and pollutant mitigation.