Optimization of Lignin Extraction from Pine Wood for Fast Pyrolysis by Using γ-valerolactone-Based Binary Solvent System

Fast pyrolysis of lignin is a promising method to produce aromatic chemicals and fuels. Lignin structure and pyrolysis conditions determine the liquid yield and product selectivity. Extraction of pine wood using γ-valerolactone (GVL) mixed with water in the presence of diluted sulfuric acid obtains lignin (GVL-lignin) which shows different product yield and selectivity. The composition of the extraction medium influences the yield of GVL-lignin and affects its native structure. The GVL-to-water ratio affects the lignin yield without significantly modifying the structure of the extracted lignin, whereas the sulfuric acid concentration affects both the extraction yield and the extracted lignin structure. These structural changes influence the products distribution after fast pyrolysis, which generates phenols and alkoxy phenols as the main products in the liquid fraction. Lignin extracted with a mixture of 4/1 of GVL/H2O (w/w) with 0.075 M sulfuric acid solution produces the highest pyrolysis liquid yield. Pyrolysis of GVL-lignin at 750 °C generates the maximum liquid yield. The amount of phenols in fast pyrolysis products increases with increasing temperature and sulfuric acid concentration used in the GVL-lignin extraction. This indicates that the extraction conditions of GVL-lignin may be optimized to increase the selectivity in fast pyrolysis

Technology overview of fast pyrolysis of lignin: current state and potential for scale‐up

Lignin is an abundant natural polymer obtained from lignocellulosic biomass and rich in aromatic substructures. When efficiently depolymerized, it has great potential in the production of value-added chemicals. Fast pyrolysis is a promising depolymerization method, but current studies focus mainly on small quantities of lignin. To determine the potential for upscaling, we evaluated the systems used in the most relevant unit operations of fast pyrolysis of lignin. Fluidized-bed reactors have the most potential. It would be beneficial to combine them with the following: slug injectors for feeding, hot particle filters, cyclones, and fractional condensation for product separation and recovery. Moreover, upgrading lignin pyrolysis oil would allow reaching the necessary quality parameters for particular applications.ISSN:1864-564XISSN:1864-563

Synthesis of Poly(N-vinylcaprolactam)-Grafted Magnetite Nanocomposites for Magnetic Hyperthermia

In this study, the synthesis, characterization, and application of poly(N-vinylcaprolactam)-grafted magnetite nanocomposites for magnetic hyperthermia are reported. Superparamagnetic magnetite nanoparticles (MagNPs) with sizes in the range of 10–16 nm were synthesized by the coprecipitation method and then functionalized with vinyltrimethoxysilane (VTMS). MagNPs-VTMS coated with poly(N-vinylcaprolactam) (PNVCL) were prepared by free radical polymerization. The obtained materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), vibration sample magnetometry (VSM), and Fourier transform infrared spectroscopy (FT-IR). The heating ability was evaluated under a magnetic field using a solid state induction heating equipment at 10.2 kA/m and 362 kHz. The MagNPs-PNVCL nanocomposites showed a behavior close to superparamagnetic materials, which is appropriated for magnetic hyperthermia treatment; in concentrations of 8 mg/mL, they were able to heat up, increasing the temperature up to 42°C in a period of time lower than 10 minutes

Isomer-dependent catalytic pyrolysis mechanism of the lignin model compounds catechol, resorcinol and hydroquinone

The catalytic pyrolysis mechanism of the initial lignin depolymerization products will help us develop biomass valorization strategies. How does isomerism influence reactivity, product formation, selectivities, and side reactions? By using imaging photoelectron photoion coincidence (iPEPICO) spectroscopy with synchrotron radiation, we reveal initial, short-lived reactive intermediates driving benzenediol catalytic pyrolysis over H-ZSM-5 catalyst. The detailed reaction mechanism unveils new pathways leading to the most important products and intermediates. Thanks to the two vicinal hydroxyl groups, catechol (o-benzenediol) is readily dehydrated to form fulvenone, a reactive ketene intermediate, and exhibits the highest reactivity. Fulvenone is hydrogenated on the catalyst surface to phenol or is decarbonylated to produce cyclopentadiene. Hydroquinone (p-benzenediol) mostly dehydrogenates to produce p-benzoquinone. Resorcinol, m-benzenediol, is the most stable isomer, because dehydration and dehydrogenation both involve biradicals owing to the meta position of the hydroxyl groups and are unfavorable. The three isomers may also interconvert in a minor reaction channel, which yields small amounts of cyclopentadiene and phenol via dehydroxylation and decarbonylation. We propose a generalized reaction mechanism for benzenediols in lignin catalytic pyrolysis and provide detailed mechanistic insights on how isomerism influences conversion and product formation. The mechanism accounts for processes ranging from decomposition reactions to molecular growth by initial polycyclic aromatic hydrocarbon (PAH) formation steps to yield, e.g., naphthalene. The latter involves a Diels–Alder dimerization of cyclopentadiene, isomerization, and dehydrogenation.ISSN:2041-6520ISSN:2041-653

Direct Evidence on the Mechanism of Methane Conversion under Non‐oxidative Conditions over Iron‐modified Silica: The Role of Propargyl Radicals Unveiled

Radical-mediated gas-phase reactions play an important role in the conversion of methane under non-oxidative conditions into olefins and aromatics over iron-modified silica catalysts. Herein, we used operando photoelectron photoion coincidence spectroscopy to disentangle the elusive C2+ radical intermediates participating in the complex reaction network. Our experiments pinpointed different C2-C5 radical species that allow for a stepwise growth of the hydrocarbon chains. Herein, propargyl radicals (H2C-C≡C-H) are identified as essential precursors for the formation of aromatics, which contribute with the formation of heavier hydrocarbon products via hydrogen abstraction - acetylene addition routes (HACA mechanism). These results provide comprehensive mechanistic insights that are relevant for development of methane valorization processes.ISSN:1433-7851ISSN:1521-3773ISSN:0570-083

Tuning the zeolite acidity enables selectivity control by suppressing ketene formation in lignin catalytic pyrolysis

Abstract Unveiling catalytic mechanisms at a molecular level aids rational catalyst design and selectivity control for process optimization. In this study, we find that the Brønsted acid site density of the zeolite catalyst efficiently controls the guaiacol catalytic pyrolysis mechanism. Guaiacol demethylation to catechol initiates the reaction, as evidenced by the detected methyl radicals. The mechanism branches to form either fulvenone (c-C5H4 = C = O), a reactive ketene intermediate, by catechol dehydration, or phenol by acid-catalyzed dehydroxylation. At high Brønsted acid site density, fulvenone formation is inhibited due to surface coordination configuration of its precursor, catechol. By quantifying reactive intermediates and products utilizing operando photoelectron photoion coincidence spectroscopy, we find evidence that ketene suppression is responsible for the fivefold phenol selectivity increase. Complementary fulvenone reaction pathway calculations, along with 29Si NMR-MAS spectroscopy results corroborate the mechanism. The proposed, flexible operando approach is applicable to a broad variety of heterogeneous catalytic reactions

Tuning the zeolite acidity enables selectivity control by suppressing ketene formation in lignin catalytic pyrolysis

Unveiling catalytic mechanisms at a molecular level aids rational catalyst design and selectivity control for process optimization. In this study, we find that the Brønsted acid site density of the zeolite catalyst efficiently controls the guaiacol catalytic pyrolysis mechanism. Guaiacol demethylation to catechol initiates the reaction, as evidenced by the detected methyl radicals. The mechanism branches to form either fulvenone (c-C5H4 = C = O), a reactive ketene intermediate, by catechol dehydration, or phenol by acid-catalyzed dehydroxylation. At high Brønsted acid site density, fulvenone formation is inhibited due to surface coordination configuration of its precursor, catechol. By quantifying reactive intermediates and products utilizing operando photoelectron photoion coincidence spectroscopy, we find evidence that ketene suppression is responsible for the fivefold phenol selectivity increase. Complementary fulvenone reaction pathway calculations, along with 29Si NMR-MAS spectroscopy results corroborate the mechanism. The proposed, flexible operando approach is applicable to a broad variety of heterogeneous catalytic reactions.ISSN:2041-172

Microparticles from Wheat-Gluten Proteins Soluble in Ethanol by Nanoprecipitation: Preparation, Characterization, and Their Study as a Prolonged-Release Fertilizer

At present, the development of natural polymeric microparticles is carried out to obtain release systems. Prolonged-release systems are a potential solution to avoid nitrogen (N) losses in agricultural fields. The aim of this study was to develop microspheres from wheat-gluten proteins soluble in ethanol 70% (v/v), to ascertain their characterization, and to study their potential application in agricultural fields. Soluble-protein extraction was performed with 1600 mL of ethanol 70% (v/v). Likewise, ethanolic solutions with protein concentrations of 0.5%, 1%, and 2% (w/v) are classified as non-Newtonian fluids with pseudoplastic behavior. Using the nanoprecipitation method, it was possible to develop urea-loaded microspheres with a diameter ranging from 900 nm–1.7 μm. The Fourier transform infrared spectroscopy (FTIR) test exhibited interaction through hydrogen bonds between carbonyls and amino groups from the urea and proteins. Also, the thermogravimetric analysis (TGA) test demonstrated thermal stability at 130°C. The release experiment showed that the microspheres achieved equilibrium when 88% of the urea was released. Finally, according to the empirical model of Ritger and Peppas, urea release is carried out through Fickian diffusion. We conclude that the microspheres could be applied in the fields and with this improve agricultural practices. Also, they could reduce the potential environmental pollution and developing a sustainable agriculture