Alkali metals (AMs) play an important role in biomass pyrolysis, and it is important to explore their catalytic effects so to better utilize biomass pyrolysis. This study analyzed the catalytic influence of K and Na with different anions (Cl–, SO42–, and CO32–) on biomass pyrolysis, and explored the influence on the pyrolytic mechanism. AM chlorides (NaCl and KCl), sulfates (Na2SO4 and K2SO4) and carbonates (Na2CO3 and K2CO3) were mixed with cellulose and bamboo feedstocks at a mass ratio of 20 wt %, in order to maximize their potential on in situ upgrading of the pyrolysis products. AM chlorides had little effect on the pyrolysis products, whereas sulfates slightly promoted the yields of char and gas, and had a positive effect on the composition of the gaseous and liquid products. Carbonates noticeably increased the yields of the char and gases, and improved the C content of the char. Besides, AM salt catalysis is an effective method for co-production of bio-oil and porous char.
This study investigated the interaction between the furfural residue and polyvinyl chloride co-pyrolysis using an infrared heating method. Various analytical techniques including production distribution analysis, thermal behavior, pyrolysis kinetic, simulated distillation and gas chromatography-mass spectrography (GCMS), and X-ray photoelectron spectroscopy were utilized to elucidate the pyrolysis characterization and reaction mechanism during the co-pyrolysis. Initially, the yield of co-pyrolysis oil increased from 35.12% at 5 °C·s–1 to 37.70% at 10 °C·s–1, but then decreased to 32.07% at 20 °C·s–1. Kinetic and thermodynamic parameters suggested non-spontaneous and endothermic behaviors. GCMS analysis revealed that aromatic hydrocarbons, especially mono- and bi-cyclic ones, are the predominant compounds in the oil due to the presence of H radicals in polyvinyl chloride, suggesting an enhancement in oil quality. Meanwhile, the fixed chlorine content increased to 65.11% after co-pyrolysis due to the interaction between inorganic salts in furfural residues and chlorine from polyvinyl chloride.
The characterization of bio-aviation fuel composition is paramount for assessing biomass conversion processes and its suitability to meet international standards. Compared with one-dimensional gas chromatography mass spectrometry (1DGC-MS), comprehensive two-dimensional gas chromatography with mass spectrometry (GC × GC-MS) emerges as a promising analytical approach for bio-aviation fuel, offering enhanced separation, resolution, selectivity, and sensitivity. This study addresses the qualitative and quantitative analysis methods for both bulk components and trace fatty acid methyl ester (FAME) in bio-aviation fuel obtained by hydrogenation at 400 °C with Ni-Mo/γ-Al2O3&Meso-SAPO-11 as catalyst using GC × GC-MS. In bulk composition analysis, C12 concentration was highest at 25.597%. Based on GC × GC-MS analysis platform, the quality control method of FAME in bio-aviation fuel was established. At the split ratio of 10:1, limits of detections of six FAMEs were 0.011–0.027 mg·kg–1, and limits of quantifications were 0.036–0.090 mg·kg–1, and the GC × GC-MS research platform had the ability to detect FAME from 2 to 5 mg·kg–1. The results showed that this bio-aviation fuel did not contain FAME.
Paper-based separator for lithium-ion battery application has attracted great attention due to its good electrolyte affinity and thermal stability. To avoid the short circuit by the micron-sized pores of paper and improve the electrochemical properties of paper-based separator, cellulose fibers were acetylated followed by wet papermaking and metal-organic framework coating. Due to the strong intermolecular interaction between acetylated cellulose fibers and N,N-dimethylformamide, the resulting separator exhibited compact microstructure. The zeolitic imidazolate framework-8 coating endowed the separator with enhanced electrolyte affinity (electrolyte contact angle of 0°), ionic conductivity (1.26 mS·cm–1), interfacial compatibility (284 Ω), lithium ion transfer number (0.61) and electrochemical stability window (4.96 V). The assembled LiFePO4/Li battery displayed an initial discharge capacity of 146.10 mAh·g–1 at 0.5 C with capacity retention of 99.71% after 100 cycles and good rate performance. Our proposed strategy would provide a novel perspective for the design of high-performance paper-based separators for battery applications.
Investigating the thermal hysteresis and its effect on the kinetic behaviors and reaction model of vacuum residue pyrolysis is of significant importance in industry and scientific research. Effects of heating rate and heating transfer resistance on the pyrolysis process were examined with the thermogravimetric analysis. The kinetic characteristics of the vacuum residue pyrolysis were estimated using the iso-conversional method and integral master-plots method based on a three-stage reaction model through the deconvolution of Fraser-Suzuki function. Results showed that the reaction order models for the first and second stages were associated with the evaporation of vapor, while the nucleation and growth models for the third stage were linked to char formation. During the pyrolysis, the thermal hysteresis led to an increase in the reaction order in the first stage, which resulted in a delayed release of generated hydrocarbons due to high heating rate and enhanced heat transfer resistance. The reaction in the last stage primarily involved coking, where the presence of an inert solid acted as a nucleating agent, facilitating char formation and reducing the activation energy. The optimization results suggest that the obtained three-stage reaction model and kinetic triplets have the potential to effectively describe the active pyrolysis behavior of vacuum residue under high thermal hysteresis.
To date, sustainable thermosetting polymers and their composites have emerged to address recyclability issues. However, achieving mild degradation of these polymers compromises their comprehensive properties such as flame retardancy and glass transition temperature (Tg). Moreover, the reuse of degradation products after recycling for upcycling remains a significant challenge. This study introduces phosphorus-containing anhydride into tetraglycidyl methylene diphenylamine via a facile anhydride-epoxy curing equilibrium with triethanolamine as a transesterification modifier to successfully prepare flame-retardant, malleable, reprocessable, and easily hydrothermally degradable epoxy vitrimers and recyclable carbon fiber-reinforced epoxy composites (CFRECs). The composite exhibited excellent flame retardancy and a high Tg of 192 °C, while the presence of stoichiometric primary hydroxyl groups along the ester-bonding crosslinks enabled environmentally friendly degradation (in H2O) at 200 °C without any external catalyst. Under mild degradation conditions, the fibers of the composite material were successfully recycled without being damaged, and the degradation products were reused to create a recyclable adhesive with a peel strength of 3.5 MPa. This work presents a method to produce flame retardants and sustainable CFRECs for maximizing the value of degradation products, offering a new upcycling method for high-end applications.
Polyolefins, widely used for packaging, construction, and electronics, facilitate daily life but cause severe environmental pollution when discarded after usage. Chemical recycling of polyolefins has received widespread attention for eliminating polyolefin pollution, as it is promising to convert polyolefin wastes to high-value chemicals (e.g., fuels, light olefins, aromatic hydrocarbons). However, the chemical recycling of polyolefins typically involves high-viscosity, high-temperature and high-pressure, and its efficiency depends on the catalytic materials, reaction conditions, and more essentially, on the reactors which are overlooked in previous studies. Herein, this review first introduces the mechanisms and influencing factors of polyolefin waste upcycling, followed by a brief overview of in situ and ex situ processes. Emphatically, the review focuses on the various reactors used in polyolefin recycling (i.e., batch/semi-batch reactor, fixed bed reactor, fluidized bed reactor, conical spouted bed reactor, screw reactor, molten metal bed reactor, vertical falling film reactor, rotary kiln reactor and microwave-assisted reactor) and their respective merits and demerits. Nevertheless, challenges remain in developing highly efficient reacting techniques to realize the practical application. In light of this, the review is concluded with recommendations and prospects to enlighten the future of polyolefin upcycling.
The loading-dispersion-reducibility dependence has always been one of the most critical issues in the development of high-performance supported metal catalysts. Herein, up to 40 wt % NiO over ordered mesoporous alumina (OMA) was prepared by co-grinding the hybrid of template-containing OMA and Ni(NO3)2·6H2O. Characterization results confirmed that the OMA mesostructure was still preserved even after loading NiO at a content as high as 40 wt %. More importantly, the reduction extent, dispersion, and average particle size of the Ni/OMA catalysts were maintained at ≥ 91.0%, ~13.5%, and ~4.0–5.0 nm, respectively, when the NiO loading was increased from 20 to 40 wt %. The catalysts were evaluated for the CO methanation as a model reaction, and the similarly high turnover frequency of 24.0 h–1 was achieved at 300 °C for all of the Ni/OMA catalysts. For the catalyst with the highest NiO loading of 40 wt % (40Ni/OMA), the low-temperature activity at 300 °C indexed by the space-time yield of methane (over 325.8
The trend of employing machine learning methods has been increasing to develop promising biocatalysts. Leveraging the experimental findings and simulation data, these methods facilitate enzyme engineering and even the design of new-to-nature enzymes. This review focuses on the application of machine learning methods in the engineering of polyethylene terephthalate (PET) hydrolases, enzymes that have the potential to help address plastic pollution. We introduce an overview of machine learning workflows, useful methods and tools for protein design and engineering, and discuss the recent progress of machine learning-aided PET hydrolase engineering and de novo design of PET hydrolases. Finally, as machine learning in enzyme engineering is still evolving, we foresee that advancements in computational power and quality data resources will considerably increase the use of data-driven approaches in enzyme engineering in the coming decades.
This study investigates the detailed mechanism of CO2 conversion to CO using the manganese(I) diimine electrocatalyst [Mn(pyrox)(CO)3Br], synthesized by Christoph Steinlechner and coworkers. Employing density functional theory calculations, we thoroughly explore the electrocatalytic pathway of CO2 reduction alongside the competing hydrogen evolution reaction. Our analysis reveals the significant role of diimine nitrogen coordination in enhancing the electron density of the Mn center, thereby favoring both CO2 reduction and hydrogen evolution reaction thermodynamically. Furthermore, we observe that triethanolamine (TEOA) stabilizes transition states, aiding in CO2 fixation and reduction. The critical steps influencing the reaction rate involve breaking the MnC(O)–OH bond during CO2 reduction and cleaving the MnH–H–TEOA bond in the hydrogen evolution reaction. We explain the preference for CO2 conversion to CO over H2 evolution due to the higher energy barrier in forming the Mn-H2 species during H2 production. Our findings suggest the potential for tuning the electron density of the Mn center to enhance reactivity and selectivity in CO2 reduction. Additionally, we analyze potential competing reactions, focusing on electrocatalytic processes for CO2 reduction and evaluating “protonation-first” and “reduction-first” pathways through density functional theory calculations of redox potentials and Gibbs free energies. This analysis indicates the predominance of the “reduction-first” pathway in CO production, especially under high applied potential conditions. Moreover, our research highlights the selectivity of [Mn(pyrox)(CO)3Br] toward CO production over HCOO– and H2 formation, proposing avenues for future research to expand upon these findings by using larger basis sets and exploring additional functionalized ligands.
The lateral dispersion of bed material in a bubbling fluidized bed is a key parameter in the prediction of the effective in-bed heat transfer and transport of heterogenous reactants, properties important for the successful design and scale-up of thermal and/or chemical processes. Computational fluid dynamics simulations offer means to investigate such beds in silico and derive effective parameters for reduced-order models. In this work, we use the Eulerian-Eulerian two-fluid model with the kinetic theory of granular flow to perform numerical simulations of solids mixing and heat transfer in bubbling fluidized beds. We extract the lateral solids dispersion coefficient using four different methods: by fitting the transient response of the bed to (1) an ideal heat or (2) mass transfer problem, (3) by extracting the time-averaged heat transfer behavior and (4) through a momentum transfer approach in an analogy with single-phase turbulence. The method (2) fitting against a mass transfer problem is found to produce robust results at a reasonable computational cost when assessed against experiments. Furthermore, the gas inlet boundary condition is shown to have a significant effect on the prediction, indicating a need to account for nozzle characteristics when simulating industrial cases.
A class of supramolecular binary hydrogels is formed from dodecylamine or tridecylamine and sparing carboxylic acids (with amine/acid molar ratio ≥ 18). These hydrogels exhibit a remarkable thermally reversible four-phase transition. On heating, they transition from gel one (G1)-to-sol one (Sol1), then to gel two (G2)-to-sol two (Sol2). On cooling, they revert from Sol2-to-G2-to-Sol1-to-G1. Additionally, several G1 and G2 hydrogels undergo thermally reversible gel-to-gel phase transitions, which are reflected by translucent-opaque and opaque-translucent changes in their appearance. The nature of the four-phase transformation was analyzed using a range of techniques. Scanning electron microscopy images confirmed that the fibers of the opaque hydrogel at high temperatures were considerably larger than those of its translucent counterpart at low temperatures. Fluorescence emission spectra demonstrated that higher temperatures, higher amine/acid ratios, and greater acid hydrophobicity increased the hydrophobic interactions. Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopic analyses confirmed the existence of hydrogen-bonding interactions and aggregation in the hydrogels. X-ray diffraction profiles indicated that the hydrogels adopt lamellar structures. The findings advance our current understanding of the phase transition of supramolecular gels and facilitate the constitution of binary or multicomponent gels, providing a practical way to create new smart functional materials.
The oxygen vacancy formation energy and chemical looping dry reforming of methane over metal-substituted CeO2 (111) are investigated based on density functional theory calculations. The calculated results indicate that among the various metals that can substitute for the Ce atom in the CeO2(111) surface, Zn substitution results in the lowest oxygen vacancy formation energy. For the activation of CH4 on CeO2 (111) and Zn-substituted CeO2 (111) surfaces, the calculated results illustrate that the dissociation process of CH3(ads) is very difficult on pristine surfaces and unfavorable for CHO(ads) on substituted surfaces. Furthermore, the dissociative adsorption of CO and H2 on the Zn-substituted CeO2 (111) surface requires high energy, which is unfavorable for syngas production. This work demonstrates that excessive formation of oxygen vacancy can lead to excessively high adsorption energies, thus limiting the conversion efficiency of the reaction intermediates. This finding provides important guidance and application prospects for the design and optimization of oxygen carrier materials, especially in the field of chemical looping dry methane reforming to syngas.
